Brantyn Gerik :
all 660 ti's and all 7770s will be roughly the same performance no matter what you pay for them.,
the only difference between different models of the same name is the cooler placed on them. this will affect heat output and noise. Generally don't worry about heat unless you have no airflow in your case, and noise is usually listed on the card specifications
650ti i think you mean... and not really...
the 650ti is roughly equal to the 7790/r7-260x, it's roughly 15% faster then the 7770. the 650ti BOOST is roughly equal to the 7850 and is another 15% faster then the 7790/260x... making the 7850 or 650ti BOOST about +30% or more faster then the 7770; and you should be able to find either for around $150
Another option would be the r9-270, which is a slightly under-clocked version of the original 7870; and which VERY closely paces the GTX 660. I've see the new r9-270 on sale for around 150 in some places (ebay) in the past week. so if you can find it for 150... that will be an even better buy then the 7850/650ti BOOST.