Alrighty. I know we're all unhappy with the state of itemization in Ulduar, but after really sitting down and looking at the situation... I'm not worried any more. Two things have changed for me:
1. After a full run-through of Ulduar I never once encountered a situation where mana was an issue that couldn't be solved through tighter play and better DP usage. (Except, obviously, Vezax, but that's entirely different scenario.)
2. After reading through several posts worth of math on the equivalency of Crit and Int compared to MP5 and applying the math within I've determined that the haste/mp5 pieces of ulduar loot have just as much if not more regen than the crit/haste pieces of naxx loot.
As best I can tell, admittedly using other people's maths, in a HL spam situation with 35 HL per minute and 1 DP per minute, 1 Crit Rating is equivalent to .5 MP5 and 1 Intellect is worth .8 MP5. For the purpose of comparing regen, I lowered Intellect to 1 Int = .66 MP5 to compensate for more realistic DP usage such as 2-3 times a fight instead of using on cooldown.
With those weightings, which rely *entirely* on spam-casting, the haste/mp5 pieces of ulduar loot such as
significantly outpace the naxx versions of loot in terms of regen while still providing much needed haste! (Comparing those two to
.) And keep in mind that any time you cast fewer than 35 HLs in 60s the values of crit and int both decrease while the value of MP5 remains static -- so any fight that involves movement (which is basically every single fight in ulduar) or that has a break in cast time (Mimiron, for example) you will find MP5 actually performing equal to if not better than crit on an item point for item point basis.
Even the tier8 haste/mp5 gear is outperforming the t7 haste/crit gear. (Obviously this is not counting the t7 4-piece bonus.)
Will it be enough to make breaking the 4pcT7 bonus worth it? That I cannot say yet. But, for me, if I can manage to remain mana neutral while utilizing these higher iLvl pieces to gain haste then that is enough of a gain for me to wear it. Mana has yet to be an issue for myself in Ulduar, and while this may change with hard-modes, if it does, the good old trusty T7 will still be in the bank ready to slap on for the ridiculous 4pc set bonus. And even then, the majority of hard modes seem to be "kill the boss faster this time!" which doesn't promise to be too straining on mana.
MP5 is still a bad stat. It's still weaker than crit and significantly worse than int. But I'm convinced that it isn't as bad as many people make it out to be, and that the combination of higher item levels and more sockets is making alot of this gear much better than was originally expected.