the 290 is a little faster then a 780, I thought the 780 would have been better ?If you already have a GTX 660 Whatever you do for Christ's Sake don't get a GTX 760.
In reality you will hardly notice the difference.
280, 770, 280X or 290.
A GTX 770 is slightly faster than a 280, a 280X has the same performance as the GTX 770 and an R9 290 is a little faster than a GTX 780.