All have the 216 core. But, like I asked before, am I going to see a NOTICEABLE different in game performance from going from a 575Mhz core clock to the 666Mhz? Or should I say, Is it worth the extra $40 to have a card with a 90Mhz higher core clock?
There's too many variables in the answer to that question for anyone to give anything but an off the cuff guesstimation. What resolution are you playing at ? Operating system? What particular game are you asking about? ... E6600 probably not overclocked..... so i'd say "3-5 fps" but it's a pretty blind guess.
The more important question is which has the best warranty/support? XFX has double (youself and anyone you sell it to) lifetime guarantee that also covers overclocking the card AS LONG AS YOU REGISTER IT WITHIN 30 DAYS. EVGA has great support, lifetime limited warranty and a step up program. Check both manufacturers out before making a choice.
Both companies cover overclocking, real world the higher factory OC'd will OC past the non factory OC'd, its like taking two greyhound one the runt and one of them the pick of the litter and training them from pup's to race, they are both dogs but they are from the same breed, just one had more potential, and 100mhz factry is nothing to wag your finger at. They all have the same cooling unit essentially. XFX technically has the "better" Warranty considering when u sell this card you can sell it with a lifetime warranty. However if your more interested in a constant upgrade go with the EVGA also look at the middle one, medium factory OC+a free game, so look at it like your buying far-cry for $20's and getting a free factory overclock,plus no rebate hassle it is the one i would choose. =)