I am running an AMD Phenom II X4 955 with an ASUS 7870 (equivalent of the 660) and I think everything greater than this would cause a bottleneck. Sometimes I think I am having one already but it is probably not too big.

Regarding the brand I can recommend ASUS too. With user-defined settings and a 30fps-limit it runs with only 44-45ºC on 30% fan speed. When I set the limit to 60fps then it only hits ~50ºC and the speed goes up to 33-36%. My old 6850 used to have a standard heat of 55ºC while I wasn't even playing a game (this one was from PowerColor).

ASUS 660

Bought mine in March 2013 for 206€ (two free Games included, aww yeah!) and now it's available for 162€ ;_;