I would go for GTX 275 which is more or less same or little expensive than HD 4890. That is one of the best card for the price and CUDA helps allot to speed up some programs like v Reveal bu working as processors.
machoo......even the 4870 challenges with the GTX260....and 4870 throws the 98gtx+,,,,
so if u want to get better performances u better than the 98gtx+ go for the 4870......wout wasting money for 4890..and if u hav the greens...then go for 4890