5750 is equivalent to a GTS 250. 4870 is wayy better card.You should consider it.
Just a lil piece advice: XFX cards are a lil more expensive than some other companies like Sapphire and Zotac. Get those as they will be cheaper.
The problem with buying cheaper cards of the same GPU is the support. I'm a loyal XFX fan and I won't mind paying $10 more for a double lifetime warranty. Haven't heard much about Sapphire and Zotac having any kind of warranty like that.