The energy regen from t9 is actually quite similar to t8.
Some knapkin math: at 2% chance to proc you need 50 ticks or 100 seconds of Rupture time to get 40 energy. That's 0.4 energy per second for t9 where t8 is 0.33 energy per second. Rupture isn't up constantly though but at 80% Rupture uptime (decent estimate on algalon) you're looking at 0.4*0.8=0.32 energy per second.
While the benefit from 2t8 is easy to scale up linearly by spreading Deadly Poison with FoK, only HAT specs can put out multible Ruptures. I'll leave it unsaid whether that's actually a good idear or not.

Off the top of my head I'd say the stat gain on the ilvl245 set is enough to warrant breaking the 4t8 bonus when you have 3 pieces of t9.

I'm pretty sure it boils down to this:

4pT8 > 4pT7 > 2pt8 + 2pT7

I don't recall whether or not the increased stats on T8 allow mixing the two set bonuses to overtake 4pT7 if you have three pieces of T8, but my gut says that they don't. Basically, keep your 4pT7 until you can start wearing 4pT8. And don't let anyone in your guild give you shit for rolling or spending DKP on T8 that you aren't using right away.

Thanks for the response.

I was under the impression that once you got 2/4 T8 you should break the T7 bonus but apparently not.. guess I'll just have to wait on the 4 piece bonus instead.

One more question.. I've always gemmed to keep the expertise cap, yet when I replace all those exp gems with AP ones in a spreadsheet, my DPS goes up, not down.

Is this something I should ignore and stay expertise capped, or as long as the sheet says I get more, should I just gem for AP?

edit: eg, I replaced 3 bright cardinal rubies with 3 prescise ones to give me exactly 210 expertise. The result was a loss of .10% DPS. Not much, but it doesn't seem to make sense to me as I thought expertise was important and going from 150 to 210 is no small amount to hit the cap.

If i have a piece with yellow and blue sockets (and also have another piece with blue socket that has better socket bonus, so nightmare tear will probably go there), guess I should just put two cardinal rubies there? No point in putting yellow gem in place if I won't get socket bonus anyway, right?

Correct, unless the value of the socket bonus is ridiculous (think Midgard Serpent level of ridiculous)

I think there are two schools of thought on this matter:

1) Gem for Expertise until you are capped because it will guarantee your Mutilates and finishers aren't being dodged, which translates into cycle stability, via more poison applications and more room to Cut to the Chase right before Slice and Dice would otherwise run out.

2) Don't gem for Expertise, and instead gem for Agility. This translates into more damage and more crits with all your attacks, as well as more damage with Fan of Knives, which does not benefit from Expertise to my knowledge.

I know many people here follow the first school, but a Mutilate rogue in my guild wearing 4pT8 felt that gemming Expertise was unnecessary, and has said that his numbers have gone up since switching all his Exp gems to Agi. I know this is secondhand, anecdotal evidence... but I think it is supported by spreadsheets, so...

You have to make a choice about which is more important to your play style: do you want absolutely reliable cycle stability, or are you willing to accept a dodged Mutilate or finisher now and then for more raw damage on everything that does land?

Good way to put it. I think in my reply the "enough" was too implied -- the rogue in my example felt he had enough simply on the gear he was using. He wasn't against gemming Expertise if necessary, he just didn't find it at all necessary with what he was already wearing, and I suspect there are a lot of Mutilate rogues who feel that way if they are wearing 4pT8 and comparable ilvl 226 offset pieces.

I was just wondering, what your opionon on is the best race for a rouge? I am horde faction.

The one you can stand looking at for 80 levels and however many hours of endgame time you play on it.

The racial distinctions are sufficiently small that it's far better to play what you'll find fun.

First of all would you care to elaborate why agi is getting a better stat than AP as the gear improves? I don't know/see why this is the case.

Has anyone done the Mutilate math? Until now I was under theimpression that AP would be clearly superior to Agionce the 4pc T8 is no longer activated due to TI, DP and Rupture only scaling with AP not Agi.