I don't think there are many games currently available on the market that can really make use of the i7's full capabilities. Heck, I don't think even Windows 7 utilizes it to its full potential. No idea how long it will be until it is commonplace, safe to assume a couple years I'd say.
Gaming quality in general is going to be by far more heavily influenced by your graphics card moreso than your processor. I'd go with the cheaper 2500k.