Gemming

[Aliveness]

Looking for advice on what gems to use for mutilate and combat.
heres what im using now:The World of Warcraft Armory
Im currently gemmed for agi for the crit/dodge, could someone explain the crit cap for me?
Ive been told to get crit capped and then go for hit then haste with mut.
and Get crit capped with combat then when i have the armor pen cap from items, gem for armor pen. Main thing is i dont know what the crit cap is but i have the formula from EJ = 100%-24% glancing blows - x%dodge - x% miss. 4.8% of crits are converted to normal above the cap. where x%- dodge = my expertise. and x% miss = my hit. Most the rogues i know use AP gems. Dont think any of them know why, if AP is better than Agi can you please show me?

Please and Thank You.

[vine]

I believe the current trend is AP gems for mutilate. It drastically increases poison damage.
Get hit and expertise capped first of course though.