What's the Best Choice?

Solution
Neither of them, go for this card instead. It is much better than the 7770 or the 640 when it comes to performance. So at that price point, you should better get this card. The 650 Ti Boost kills both of them.

PCPartPicker part list / Price breakdown by merchant / Benchmarks

Video Card: MSI GeForce GTX 650 Ti Boost 1GB Video Card ($109.99 @ Newegg)
Total: $109.99
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-07-22 04:18 EDT-0400)

You can close the post anytime when you find the answer you were looking for by selecting that answer as the best answer.
Neither of them, go for this card instead. It is much better than the 7770 or the 640 when it comes to performance. So at that price point, you should better get this card. The 650 Ti Boost kills both of them.

PCPartPicker part list / Price breakdown by merchant / Benchmarks

Video Card: MSI GeForce GTX 650 Ti Boost 1GB Video Card ($109.99 @ Newegg)
Total: $109.99
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-07-22 04:18 EDT-0400)

You can close the post anytime when you find the answer you were looking for by selecting that answer as the best answer.
 
Solution