Get the best card you like ... don't worry about CPU Bottle neck , Cards can move to other PCs ..
and don't get 660 Ti , get the new GTX 760 it is faster ,
if You can get even the better GTX 770
and btw , Pick Nvidia it has PhysX and it is waaay cool.
here is an example of what you will get with PhysX http://www.youtube.com/watch?v=F1ZHfJRrFLU
and Ramadan Kareem