Hey there!
I've been playing a death knight since the release of Lich King, and I can be called a DPS Theorist in such ways... and especially with Frost DPS... partly because I enjoy it the most and I have gotten crafty and innately reflexive with how it operates in different types of battles... etc, etc. But also because I'm practically 1 of 5 good Frost Death Knights on our non-PvE server.
I've been reading the initial post, and I can see that you all have really worked hard to categorize and explain this art of Deeps, because frankly, I couldn't explain it for the life of me :P
Anyway, onwards to srs bznz. Like I said, when you become "innate" to your class as if it was your second nature, you can tend to be drawn the "familiar" way of doing things... aka, You can always be good at the spec you're used to (even if it isn't mathematically the best), and you suddenly lose your skill when you change into another. (I can't get Unholy down, but it seems to be all the rage here in 'da hood)
My point being, I've been a Frost DPS for upwards of nine months now, and I don't see myself switching for a long while, but people still ask why I play the way I do. My spec is 3/51/17 (3/3 in Subversion, 2/3 in BCB) and always has been. For my own Simplicity, I skip Deathchill and Unbreakable Armor, only for the reason that I'm lazy and don't want to watch my buffs every 15 seconds. I use Unholy Presence and Glyph of HB.
I'm only online right now to theorycraft about why I choose these two elements of my class, and willing to recieve any explanations, criticism, death threats, etc.
[Glyph of Howling Blast] - Allows the Howling Blast ability to cause Frost Fever.
I chose to apply this glyph rather than 3.3 Glyph of Icy Touch (20% FF damage). I see that Icy Touch is a general part of a 3.3 Frost rotation (or so you say) but I think differently. Since the power of Icy Touch is only minimal, I can override spending the frost rune on refreshing the disease I already have up, and instead keep the uptime of Frost Fever 100% just in the Rime HB proc. I never need to worry about refreshing FF since its already a part of my rotation, see? And because of 3/3 in Blood of the North (tier 8 of Frost tree) my extra Frost runes are actually and always Death runes. And of course, with DR I can use a free Obliterate. Mmmmm damage. Any thoughts on this?
Unholy Presence - Infuses the Death Knight with unholy fury, increasing attack speed by 15%, movement speed by 15%, and reducing the global cooldown on all your abilities by 0.5 sec.
Also, I'm going to explain why I personally think Unholy is a still-viable DPS Presence both on long, slow, single-target battles (Saurfang) - AND on fights where you must move around a lot to kill frequent adds or get outta dodge of the large fire the boss just put on the ground... again.
Here is a simulation of my Frost DPS in Blood Pres.
BBfFuU - 0 sec - Howling Blast - 15 RP (Assuming that I didn't use HoW before the battle)
BBfFuu - 1.5 sec - Plague Strike - 25 RP
bBfFuu - 3 sec - Blood Strike - 35 RP
bbfFuu - 4.5 sec - Blood Strike - 45 RP
DbfFuu - 6 sec - Blood Tap - 55 RP
dbffuu - 6 sec - Obliterate - 65 RP
dbffuu - 7.5 sec - Frost Strike - 33 RP
dbffuu - 9 sec - Frost Strike - 1 RP
This brings us back to the beginning, but with a 0.5 delay to the active runes. PLEASE NOTE: The first HB may seem like a wasted rune/glyph, but with 3/3 in Rime, I am able to successfully keep the uptime 100% without consuming runes... The problem is, I can't suitably use Howling Blast, while other runes continue to be available. HB is not prioritized over Obliterate, but I am using that certain GCD having to reset my FF. Applying Glyph of Icy Touch only makes it worse. Since it frees one Unholy rune, I can't help but cast an Obliterate between PS and BS (see diagram above), which ultimately delays the runic system by another 1.5 seconds.
Also note that after every cycle the 10 second rotation (I know its not a rotation. I'm just giving it a name) - I am able to use an ability again relatively 10.5 seconds (if my timing is optimal) after first using the runes. This means that after 30 seconds, I can reset my "cycle," not even using the last 1.5 seconds for a final move. This ultimately means that after 30~ seconds, I will have the runic power for a FS and never be able to use it in a fight. Ever.
NOTE: This is tested against a dummy THOROUGHLY. I used Empower Rune Weapon in my other simulations. After one minute of attack, my Runic Power was completely full, and it remained that way the entire battle. Frost Strike had a striking 1100 of my total DPS (Which was around 4500 in my gear), but only 12% of my total damage.
The only drawback to Unholy Presence is that nasty downtime while all your runes are unavailable. But you can learn to use that downtime to gain runic power via HoW, or pop a Blood Tap right when it becomes available. Plus, ERW will prove to be an excellent ability in Unholy, since it allows you to reset your priority, fill up your Runic Power pool, FS-spam it up, and your other runes will start popping again, almost religiously so.
Any thoughts or "I can prove you wrong" epiphanies? I'm open to new ideas.