Depending on the game , CPU demanding game like BF3 will lag from time to time due to CPU bottleneck . He definitely need a multi core (4->8 cores ) CPU for that game . Most modern PC games support multi core CPU , some games even support Intel Hyperthreading (Quad i7 will kill Quad i5 at this point)
Laptop: (Show Spoiler)
Mini PC :: (Show Spoiler)