that card will be a significant improvement but your processor will hold you back quite a lot. high end games are out of the question unless you can tolerate 20fps or less. i found a review that shows your processor with a gtx 590, only getting 30fps, and your new card is 1/4 that one. but your processor is whats holding you back so im guessing that you will get in the low 20s.
you should check your motherboard, you might have a cpu socket that you can shove a cheap athlon x4 or phenom II into. you can get them pretty cheap new and 20%-50% cheaper used.