A 2500k sitting @ 4.5 ghz will be faster than a stock 3770 when it comes to gaming. The gap from Sandy to Ivy is pretty minimal and for gaming it's even smaller than that. Yes the 3770 is the superiror chip for all around compute jusr for the fact it's slightly faster thread for thread and is equipped with hyper-threading. But from a pure gaming stand point an OC 2500k >stock 3770.
There will be certain games that are highly threaded that may make sue of the HT on the I7 and in those cases the 3770 may break even or be slightly faster. However thats pretty rare at this point.