Just google that model of vid card to check reviews. Sites like http://www.tomshardware.com
frequently post comparitive reviews of video cards so that you can see how that card stacks up against an Nvidia of a similar price.
As far as performance, your processory, memory, motherboard and also, to some extent, your hard drive are going to affect the degree of detail you can squeeze out of any given game with any given video card. You can't compare two video cards directly unless you set them up with identical test beds, so your results will differ from what other people get unless they have the exact setup you have.