Not knowing the rest of your build, the performance of the GTX660 or R9- 270 will be similar.
It would take a synthetic benchmark to tell the difference in most games.
The graphics card is all important for gaming.
You might budget twice the cpu cost for your graphics card.
The nvidia cards seem to run cooler and quieter than the equivalent R9 cards.
I don't think it is worth it to pay more for a 3gb vram card vs. 2gb.
Here is one study:
http://www.pugetsystems.com/labs/articles/Video-Card-Performance-2GB-vs-4GB-Memory-154/
save the money, or see if it helps you to a next higher tier like a GTX760.
The stock blower type coolers from EVGA are very effective. No need for paying more for fancy aftermarket coolers, spend the difference on an intrinsically better performing card in the first place.