Weapon specs apply on a per-weapon basis regardless of what the character sheet tells you. So, the answer is yes.

That would only work if weapon speed somehow would be tied to the item budget for stat allocation, i.e. a faster main hand weapons can have more stats added to them (or vice versa for off hand).
But as it stands now, given equal DPS and ilevel, slower = better for main hand and faster = better for off hand. There really isn't much to think about at the time being.
Or has there ever been, besides broken mechanics like Shiv spam (Combat) or poisons spinning out of control (Mutilate).

So I've finally saved enough to be able to afford the Darkmoon trinket, but with the patch likely coming out before the next darkmoon turnin period (april 6th), and I'm wondering if it would be worth it to invest in a noble deck for use in 3.1.

Wrathstone
Pyrite Infuser
Melee equivalent of Eye of the Broodmother?

vs.

Darkmoon: Greatness

If its second or a close third for best in slot it would definitely be worth it to drop the dough on it, but otherwise I'd rather save my money for some of the BoE items from uldar.

As the items have no tested or stated cooldowns, some assumptions have to be made. I used a very rough assumption model - for on hit procs (such as Greatness, and one of the two states of Wrathstone) I just assumed it would proc every 50s on average (45s internal cooldown), and used a 2min cooldown for the on-use trinkets. I also pulled the EP values off the Handbook, assuming that you are over hit cap in both cases. With those assumptions DMC:G comes out to be 420 EP for both specs, Wrathstone (Chance on hit) is 515.2 for mutilate / 504.4 for combat, Wrathstone (On use, 2min CD) is 315.5 for mutilate / 304.7 for combat and Pyrite Infuser (50s average interval between procs) is 379.8 for both specs above the poison hit cap.

Edit: Changed the numbers for Pyrite Infuser

Speaking only for Combat Spec Rogues, and how we interact with itemization I have a few key points to bring up speaking of Ideal itemization for Combat Rogues.

ATM the BiS combination for released gear still stands to be CFD(Combat Fist/Daggers) using Respectively
Golden Saronite DragonMH
Golem-Shard StickerOH

After that you have a few viable combinations using new gear. They are as follows.
Combat Fist/Fist using MH Golden Saronite Dragon/ OH Kinetic Ripper

Combat Sword/Sword Using MH Malice/ OH Rune-Etched Nightblade

And using Ranged Siren's Cry currently appearing BiS out of all possibilities by Stat allocation.

An Interesting thing to note would be what the actual variance of DPS for such things as Remorse compared to Rune-Etched Nightblade.

Now most might say its a cut and dry decision but based on how Combat Spec factors OH itemization its not as simple as it may appear. Using general rules for OH DPS speculation you would put Rune-Etched Nightblade at 183 DPS compared to Remorse a 178 DPS base item. Not such a big overall dps difference as it stands already. That is mainly do to the fact Remorse is 13 ILvL higher than Nightblade. But what really comes to factor in now is how much DPS do you gain from Poisons with new PPM System for having a .20 slower item. Also note that Remorse has a higher general Stat allocation from ILVL off the bat. If in fact the dps gained from Poisons for .20 slower is in the range of 6-8 DPS it is quite possible for Remorse to be BiS for sword spec over Nightblade. Much testing would be required.

That also allows me to bring up Stonerender a 178 1.60 mace. I did not mention this because it has no Current MH partner to be released to date. That does not however change that fact that given another Fast Mace also in lines with Nightblade and a Good MH that it couldn't also become BiS.

On all of these notes any combination different than Saronite/Golem ATM is lacking due to the itemization of those 2 items. Golem being a 1.50 Item at 178 DPS better than anything we have seen and Saronite being a 188 DPS item also far better stated than any other available/released items to date. I will do some general testing on the PPM mechanics for poisons, with the 2 following items on PTR in hopes to come to a general conclusion as to DPS gain by slower items compared to faster. Using WD/Split Greathammer comparatively only comparing Poison dps over 5, 6 Minute Attempts using the separate items in MH only.

Two new 1.8s daggers found today:
[Daschal's Bite]
[Shadowbite]

They aren't on Wowhead yet, but posted today fro MMO-Champion:
http://static.mmo-champion.com/mmoc/...h/03_25_12.jpg
http://static.mmo-champion.com/mmoc/...h/03_25_26.jpg

Dashal's at 232 ilvl replaces Sinister Revenge as the best known mainhand currently available.

Along with the daggers, there were a couple more items found as well:

Belt: http://static.mmo-champion.com/mmoc/...h/03_25_15.jpg

Neck: http://static.mmo-champion.com/mmoc/...h/03_25_25.jpg

Dropped from Trash (25) and General Vezax (10) respectively.

You are correct, I must have been half-asleep or something. Using the same weights with a 50s average interval between procs nets 379.8 EP.

Not that it's important, what with Ulduar on the horizon, but the common conception that Hailstorm and 4/5 sword spec is higher DPS than Webbed Death and CQC+fillers as Combat seems to be false; I can't find any combination in the spreadsheet including best-in-slot options in which this is the case.

Sorry if this was already noted somewhere in the black hole of Rogue theorycraft, it's just been something that I've been trying to figure out since I've started playing Combat recently, and I'd just like a bit of confirmation on this from other posters: have others found the same thing?

Hmm, with 2/5/5 CG/Hailstorm seems to be superior by 5 dps, with BiS, at 300 duration, 11 dps with 0 dps.

This is with all buffs, human, heroic presence, Stalk-Skin and Dawnwalkers (oddly enough with the exception of 1 precise, full ap seems better and not having expertise capped). Also Footwraps of Vile Deceit seem to be a downgrade.

However the difference is minimal and, as you say, irrelevant in 3.1

Yes.