I don't think new computers would come with 5650 anymore.
GTX260 doesn't support DX11, no use buying it if you want to
play DX11.(even if you don't now, you might in the future)
DId you have to mention 5750? -_-
I'm referring to the 5670.
GTX260 is for those who don't care about DX11 (5750/5770 both
suffer with DX11 by quite a bit compared to DX10/.1 mode) and want
more power. And why do I have to mention 5750? Because it's
relevant.
Also, GTX260 has PhysX, if you want that eye-candy. I personally
don't give a hoot, but hey, you might. Your friend(s)
might.