20% ICC buff = blue gear turns into EPIX

Or not...
This was one of the arguments pointed out on the video of the Marrowgar kill and in some responses to Gevlon's post. Comments such as: You dont need to be a math genius to understand that the 15%-Buff compensates the lack of gear.

ilvl200 avg gear + 30% ICC buff you be equal to what ilvlgear in your opinion? The logical thinking would be ilvl260 avg gear, but would that really translate in ilvl260 dps/heal/tank?

If we are naively to assume that the value of each stat is 30% better under the buff, then you would have something like a 260 iLvL rare item

To get a solid answer, I put up two profiles in Rawr, one with my current tank gear + all the buffs we use + 20% ICC buff. The other was a mixture of ilvl 232 gear, with some items lvl 226 and one at 245, + all the buffs we use, but NOT the 20% ICC buff. Both profiles had the Chill of the Throne debuff (-20% dodge) I used epic gems with the latter profile, but same enchants on both.

The numbers look like this:
Blue gear:
Hp: 46658
Armor: 26249
Defense: 541
Dodge: 0%
Block: 16.56%
Block Value: 1344
Parry: 15.88%

ilvl 232 Mix:
Hp: 49832 (+3174)
Armor: 28963 (+2714)
Defense: 550 (+9)
Dodge: 2.70% (+2.70%)
Block: 15.40% (-1.16%)
Block Value: 2230 (+886)
Parry: 19.65% (+3.77%)

Seems I should have chosen a bit lower lvl gear than 232 ilvl...
Anyways, it seems to me that with the 20% buff, blue tank gear translates into roughly Ulduar gear (226-232-ish), at least HP-wise. The other stats, such as dodge and parry would still be significantly worse than any epic gear, since the buff only affects total health and dmg done.
And of course, this only applies to tank gear, I have no idea how dmg/healing gear would scale with the buff.

So there you have it! I'm gonna put this info into my next video.

I had to, so I made yet another profile with 219 - 226 ilvl gear. The hp is similar, but the other stats are still better:
Hp: 45142
Armor: 26961
Defense: 540
Dodge: 2.06%
Block: 20.31%
Block Value: 2238
Parry: 18.90%

Out of interest, I've made a similar comparison for the Survival Hunter. Keep in mind that at high gear levels, Marksman will pull ahead, so the actual difference is even larger.

With all relevant buffs and debuffs checked, my maximum theoretical DPS would be as follows:

• Blue Gear: 4764
  
• Blue Gear +30%: 6193
  
• T7 Gear: 6128
  
• T10 Gear: 13630
  

With T7 items including all items available from Naxxramas, Sartharion and Malygos, with epic gems and optimal enchants allowed. Items of comparable item levels but from later content (such as Ulduar, ToC5, ICC5, Conquest Badges) are not allowed. See here.

The DPS value for T10 BiS gear was taken from this topic on EJ.