Purified Twilight Opal (9+8*0.21=10.68/ 19 if used in headslot or if you need it for the meta) for Metagem
in some situations where you need the 2 blue gems for the meta but the blue socket boni are crap, you can put a Misty Forest Emerald (8*0.61+*0.21=6.61 /14.93 if you need it for the meta) in it. The value may look a little low, but with a socket bonus like 8 crit in a yellow socket(most helms have that bonus) it's better thanPurified Twilight Opal.
Chaotic Skyflare Diamond (40.34+21*0.61-16.64=36.51)
Math of CSD: (Thanks to Mefadin)
But the 3% Increased Critical Damage actually translates to 4.5% extra damage on crits(this isn't different, but is often unclear) and there's a big difference between the amount of crit damage at 70 and the amount at 80. Going by the baseline output file of SimCraft from http://code.google.com/p/simulationcraf
... 80_General, MB/MF(/SW
) make up
60% of damage and are crits 40%(or better) of the time. 4800 DPS * 0.6 * 0.4 * 0.045 = 51.84 DPS ~= 40.34 PP. Even using less optimistic values of 3000 DPS * 0.5 * 0.3 * 0.045 = 20.25 DPS ~= 15.76 PP, which would be slightly less valuable once socket requirements are taken into consideration, but it's unlikely to have 1k int and only pull those numbers.
CSD requires at least two blue gems. To ensure this requirement is satisfied, helm will be calculated assuming the red gems elsewhere are replaced by blue gems (loss of 16.64 PP)