Don't go 650. I could run through all the mubojumbo but Tust me, 570 kicks a 650s booty. 570 is a bit more than twice the performance of a 650.
Just cause 650 is higher than 570 doesn't mean its better. First number is the series and the following numbers is that cards performance relative to other cards from the same series. I had a friend who (Back when I had a GTX 260) thought his 410 was better than my card cause the overall number is higher.
650 is upper low end and a 570 is midrange of high end Cards.
Hahaha It's funny you say this. I tried to explain this to my friend, but he wasn't having any of it. He just kept saying that "The clock speed is higher! The memory is clocked higher! It's obviously better!"
I think he was in the mindset of "Higher number = better card"
I tried to explain the concept of bus width, bandwidth, number of units, etc. etc. I just had to make sure I wasn't crazy.