yea, wow is pretty cpu limited, when i got my new athlon II x4 even with my old crappy 8500gt there was a noticabel difference over my old socket 939 am64 chip .
whats your whole system like?
my wife had a hd 4670 that we jsut replaced with 2 x gts 450's in sli which should run wow perfect but due to her cpu being a old single core we got zero improvment (was not expecting any, but she wanted the gpu's before the new cpu/mobo because she thoguht her cpu was good enough and what do i know)
that card should be able to play wow depending on the res at medium settings with a good enough cpu and at least 3 gigs of ram (pref 4 gig + ... and yes wow will saturate that much ram)
^ yes it'll give you a nice uprade and you should definatly be able to get beyond 800x600 with that card maybe 1280 x 1024 with medium settings