Are there any specific EP values for items here or is it more of a personal per-item thing?

An EP system would imply a single output metric (e.g. DPS). Healers have at least two (throughput and longevity), and weighing the two is not something that can be done with a great deal of accuracy (you end up making a whole pile of assumptions about what fight you're talking about, so while you could say that, for example, 1 mp5 is equivalent to N spell power, that N will vary depending on the length of the fight, the exact damage pattern, your exact spell rotation, some assumptions about how adding 1 of each stat will affect certain talents, and so forth).

And it's my personal opinion that this question does not belong in the simple questions thread because it doesn't have a simple answer.

Tattersail

Here is some info from my guilds first 25man kill of sapphiron. It wasnt my best fight by far numbers wise, but here is the info from it. Overall I was at 37% overheal (our OT respec'd holy for the fight).

13min40sec fight:

Power Word Shield Cast on MT 25 times (5569 Absorb per shield)
Damage to MT
1,106,026 Physical
302,148 Frost
80,818 Shadow

1,488,992 Total Damage
200,744 Absorbed or 13.48% Overall
5,569 x 25 = 139,225 Absorb from PW:S 69.35% of damage Aborbed
61,519 Absorbed thru Devine Aegis 30.65% of damage Absorbed

Looks like I was criting around 28.5% of the time.

I am trying to assess usefullness of discipline build as well. There is way to distinguish between shields fully absorbed and shields that are used only partially, but as to amount of absorbed damage if it is not full it is mostly very fuzzy.

Fully absorbed shields are easily calculated by looking at start of power word:shield buff and its end. If it is less then 30 seconds, it is always fully absorbed shield. To accomplish this, just import text data of the log as obtained by wow into any sort of relational database (I am using MS SQL server) and filter it for Power Word: Shield. Then sort it according time and there is clear sequence of SPELL_AURA_APPLIED and SPELL_AURA_REMOVED records.

I am missing a lot of 'absorbed' records in the log though and that is true even for the shields, that have been removed 5 seconds after appearing. I suspect that logs actually miss the data. Question is though, whether they are missing from the log only, or whether shield mitigation is bugged. (I would say that former is valid)

What is quite clear is the amount absorbed by full shield. Results are showing that having approx 2250 SP raid buffed shielded value is approximately 7000.
With heal of approx 1300 gained from the glyph, effect of the shield is comparable to Greater Heal.

You mean in effective healing done? Effective healing done should pretty much always be higher for multitarget raid healing, so it's not really a valid comparison.

Post 3.08, the question is more how holy priests compare to shamans and druids at raid healing. I'm not sure anyone knows for sure, but it certainly won't be so easy for priests to always top the meters.

Yes, there are several hitches that make it fairly painful to figure out absorb damage. Here's a basic synopsis of how I have done it:

1. Modify the log so it's easier to import into a database. Mostly the date header is different from the rest of an event line by being delimited by something other than a comma, so I delimit all fields with commas. Simple text seaches with replace can do this. Some database import tools might be able to do this as well.
2. Import the log into a database.
3. Select all SPELL_AURA_* events where the spell is "Power Word: Shield". Dump the query into a spreadsheet.
4. Select all SPELL_AURA_* events where the spell is "Divine Aegis". Dump the query into a spreadsheet.
5. Select all *_DAMAGE events where the absorb parameter is >0. Dump the query into a spreadsheet.
6. Select all *_MISS events where the absorb parameter is >0. Dump the query into a spreadsheet. [Some people fail to realize fully absorbed hits come out as MISS events, not DAMAGE events].
7. Add some columns to your SWING_ and _MISS spreadsheets so that the absorbed columns can line up with spell and ranged damage spreadsheets.
8. Paste all the source spreadsheets into a bigger spreadsheet
9. Create a new time stamp column which modifies the times for SPELL_AURA_ events. Because events can arrive out of order, you want to make it look like buffs are applied earlier and expire later. I modify them by 1.0 seconds.
10. Sort by the target first (!), then the modified timestamp.
11. With a little luck, the vast majority of absorb events will now be bracketed by buffs applied before and after the absorb events... but unfortunately, that might not always be true.
12. There are a lot of potential ways to proceed from here that might save you time. What I did was add columns for DA and PWS that tracked the state of that buff as well as who applied the buff. When no buff was up, the column is blank. I also added two columns to hold the amount absorbed by DA and PWS, respectively.
13. Now the fun begins since I know of no reliable way to go from here besides inspecting the spreadsheet and crediting the absorbed damage appropriately. Fortunately, most the time it's very obvious, but you'll see a variety of weird cases that require a little thinking.
14. I found that at least most of the time, general DA shields are absorbed before PW:Shield, even when the DA buff occurs after the PW:S buff. So when both buffs are up, the absorbed damage is usually assigned to the DA shield. But you can tell by seeing that the DA buff is consumed before the shield.
15. Sometimes both buffs may be up, and a hit will break through one shield and then be absorbed by the next. This will be apparent because the hit is fully absorbed (it's a miss event), but one buff fades (usually DA) while the other one does not fade. In these cases, I split credit in a 2:1 ratio with more credit going to the PWS. Don't stress over this since it's a rare event, but if you look over the data, that's a plausible ratio since DA shields are usually much smaller.
16. Once you get done going over every line in the spreadsheet, swear at Blizzard a while for failing to make this easier. It's a cathartic experience.

It's painful, but this produces pretty accurate results. Although there's some guesswork involved whenever two shields are up and a hit breaks through one into the other, there's enough context in most cases to get a reasonable estimate on those. For instance, you'll see that most DA shields absorb a similar amount. So when a hit breaks through it and into a PW:Shield, you know the DA shield was fully absorbed and it absorbed about what other DA shields from that priest would. If you apply a little reason, you won't be off by much on those.

The bigger problem IMO is that the combat logs are not timestamped with the time that the event happened on the server. The timestamp is when the event arrived on the client. That's messed up because network packets arrive out of order and give you "impossible" sequences of events. For instance, here's a real sequence from one of my combat logs:

So what that basically says is that:
1. Promethiaep put a PWS on Makmooka.
2. Makmooka aborbed 280 (??) of the next hit and the rest was damage.
3. Makmooka absorbs 5362 and takes no damage from the next hit.
4. Promethiaep procs a DA shield on Makmooka which simultaneously fades.
5. Makmooka aborbed 1567 of the next hit and the rest was damage.
6. Promethiaep procs a DA shield on Makmooka which simultaneously fades and PW: Shield simultaneously fades.

Sort that one out. The only lucky part is that if all I care about is who to credit the absorb damage to, then I'm probably ok, but imagine if those buffs came from different priests!

I hate to be a stickler but this is not true for one case. If you overwrite your pws with another pws before the end of the duration of the buff.

just a tiny question, what do u guys think is the best(better) for general all around usage of the food buffs currently available for a 14/57 holy priest

I may just wade through a few 10-man WWS with me being the only Disc Priest and tally up all the absorbs. Now I was wondering if there any absorbs from other classes that could interfere. Do any tanks have any absorb effects? Does WWS count black as absorb?
I'm only aware of Mages and Warlocke being able to absorb some damage, so I'll check for their buff gains.

Any other input into what I may have overlooked could be good.

There is a tank trinket that creates a shield.

Cuttlesteak for regen, imperial manta steak for throughput. But that's more a question for the "simple" thread.

A few trinkets create shields. [Essence of Gossamer] and [Noise Machine]. Also any other healer with the [Scarab Brooch] will be creating absorption, although that is unlikely.

The only other absorption effects I can think of are a Paladin's Sacred Shield, Anti Magic Zone, The Shadow, Frost, and Fire Wards, [Greater Ward of Shielding], Voidwalker Sacrifice. But I'm sure there are plenty of others.