Well you didn't tell us how much this swap will cost you, but yes you might see a difference in game preformance. The processor is deffinately better, but your not going to see a dramatic boost in FPS, unless the game can make use of 6 cores and hyper threading, which is basically no games right now.
where did the 6 core come from?
OP: if he will sell it to you for very cheap or you sell your i5 so the net transaction puts you back about $20~40 then sure, otherwise it's not worth the money. All you really getting is the hyper threading on the i7 vs i5 and 0.1ghz stock frequency. As far as I know, very few games benefit from HT if at all (many claim that HT actually decreases CPU performance in games)http://ark.intel.com/compare/52209,52213