i7 is of course better than i5, but because the GPU (while better than I had thought) is still not that great, most games are going to run into trouble with the GPU. For that reason, getting an i7 probably isn't worth it, because almost no games are going to need that good of a processor with a GTS 335m.
I don't think it's worth it, i5 is already great and i7 would make your computer pretty out of balance.