Using EJ's listings; the most 50 crit is worth is 47.5 EP, while 22 AGI is worth at minimum 57.2 EP. EP is the general guideline on what stats are worth, so the more EP the better average DPS.
Heck, even the 65 crit isnt much better. For assassination, you get 57.2 EP from 22 AGI, while 65 crit(which I dont think anyone on my serve even seems to have) is only worth 58.5. So at minimum, you should switch the worth/value for the enchant on cloaks for rogues, so that 22agi is above 50 crit for all specs.