It's hard to say, since Agi adds to your crit chances, improving the amount of bonus CP's you generate yourself.

On top of that:
Sinister Calling and Deadliness stack. So 100 Agi translates into 115 Agi from SC, adding 115 AP + crits, which translates into 126.5 AP through Deadliness + crits. While 200 AP translates into 220 AP through Deadliness.

Stat weights are definitely different for HaT builds, but it's hard to say what they are exactly, since modeling HaT to figure them out is way too much work (for now). It might be more towards AP by default, but the stacking of Deadliness and Sinister Calling, and your own CP generation through crits seems to even out this offset again.
The only combat stat that I can tell which is definitely of less value to HaT builds would be Haste, since it provides no energy regeneration like it does for Mutilate and Combat builds.

HaT specs are basically uncharted territories, and theorycrafting is staying away from it for now, since it's
a) too hard to model, given all the other things that still need modeling. It's basically at the end of a long wishlist.
b) assumed to not be on par with Combat or Mutilate builds, since the finishers used have no Weapondamage component, while combomoves do. Weapondamage improves more than weapon statbonusses do, so it's basically assumed that standard combomoves will take over from finisher spamming pretty soon.
c) HaT specs rely on the crits in your party. It will take a little while to get the awesome critrates we had in the final days of TBC back, and it's assumed that (b) will have taken place by that time.

Which is basically the same as asking for a magic number. Stop miring yourself in this type of thinking, it is wrong and bad. Get the gear that is indicated to provide the most DPS by spreadsheets or other tools, and gem for the stats that provide the highest DPS per point. Your resulting stats will be what they will be. If you aim for magic numbers you are always doing it wrong.

I really hate asking stupid questions, and I know a lot of Rogues are going to rightfully roll their eyes at this, but I've tried to figure this out for a long time and I cannot.

I specced 5/5 CQC, fist mainhand, dagger offhand.

If I remove the fist and substitute any other weapon type in its place in the mainhand slot, I lose approximately 10% of my crit. It seriously goes from 28-29 down to 19%. I lose nothing when unequipping the offhand.

Is it a tooltip error?

Are you using a weapon you have maxed your weapon skill on? If not you will have lower crit till you get the skill up.

It was slightly, but now that's remedied. Even at the worst it was 15 points or so under from 365, which was my max. Awful small margin to be 10% crit, isn't it?

I can't check my armory at the moment or I would.

Based off of what I've seen of stats displayed on the character sheet I would say this is a tooltip error. All damage and crit % are based off of your MH (unless you hover over weapon damage, then you see your OH Damage).

Since hovering over the crit % only shows your crit rating converted into % there is no diffierntation between MH and OH for this. I suspect that once you no longer have a fist/dagger in the MH, the tooltip fails to recognize the 5% crit of your OH dagger even though it's there with that weapon.

Hope this helps.

It does, and I appreciate the observation. I did some dummy testing and did not find my crit decreased by 10%, but closer to 5% as well.

Just very unnerving to see a 10% crit drop from unequipping that fist.

Mut question:

I spec'd Mut with only 1/2 SnD and the SnD Glyph. I felt that the uptime with 2/2 SnD is just too much, I find myself using Envenom with about 10-12 seconds remaining on SnD, with Rupture going already.
The problem I'm encountering is what to do with the spare point. I was considering just putting it into CQC or TtT.
However, theres times when Im sitting around waiting for my DP to stack, and watching my energy cap out for 3-4 seconds or more. Would It be wise to use the spare point and grab Vigor(which I and many others have considered ineffective investiture for raiding) which would allow me to pool my energy a bit longer without waste, so that right after I get DP stacked I can get a guaranteed 2x Mut and HfB refresh?

I considered refreshing HfB before things like this happen, however I've only found that in my rotations, I only really have 2 opportunities to refresh, at about 14s-15s, and about 1s-2s remaining. It's cutting it really close.

tl;dr: The energy drain from 2x Mut after Envenom is leaving me with too small a window to refresh HFB. Should I invest 1 point into Vigor(20E with glyph) to solve this problem?

side note: I think whatever saved energy not spent on cycle like this might also be used on Mut's at 4CP, turning them to 5, in essence, for free.

Really tired, sorry if it didnt make any sense.

Combat Question:

What are your thoughts on finishing at 4 combo points instead of 5?

Raid-buffed most rogues are at 35-40%+ crit, so if you perform another sinister strike at 4 points you have a ~20% chance of "wasting" a combo point because of the sinister strike glyph.

I have just turned 80 and am working on my pre raid gear for 10 mans. I have been given 2 Librarian's Paper Cutters which are 1.3 speed. Now I understand that my mut crits will be lower because the top end damage is less then other daggers with slower speeds. From what I've read though, the faster speeds will allow faster poison damage and faster attacks which may actually increase my dps. So when I am looking at my spec, do i want to take all the poison associated talents? What talents are crucial and which are not so important? Should I still take lethality?

If this has been discussed before please point me in the direction.

It has already been discussed in any of the innumerable "what's the best spec?" questions that have been asked.

Something similar to this is most likely what you're looking for. To answer your exact question yes, you do want all the poison talents.