http://www.techspot.com/review/577-borderlands-2-performance/page2.htmllooks like it doesn't take a super tier GPU to run so your GTX 650 Ti will be more than enough I imagine
http://www.techspot.com/review/577-borderlands-2-performance/page6.htmlbut it looks like your CPU will bottleneck you, it's under the Phenom II X6 but should still be stronger than any of the FX's (since Borderlands mainly relies on single thread/core performance)
all in all, it looks like you should be able to run it at your resolution at Max settings, rather than high, at around 45 ish fps, and should be able to smoothly run high at around 60 fps
this is all speculation and guessing through benchmarks, since i've never played the game, so it may not perform as i say or as you want