I'm going to give you a very basic answer here. In titles that are processor specific, games that utilize up to but no more than two threads, the Pentium will have a clear performance advantage. Whereas any processor bound titles that are well threaded and can make use of more cores, logical or otherwise, will perform better with the stock i3 in theory.
In those well threaded games, the average frame rate will likely lessen a touch, but not much. The minimum frame rate will take a pretty decent hit. And that's the concern for gaming