Intel has better performance per core, and most games are optimized only for 2 cores, and in addition may have some spec. optimizations for intel - So not many games can fully use potential of quad core CPU specially from AMD, on other side your cpu is bottlenecking that gpu a little. World of Tanks, Diablo3/SC2, Assassin's series and so on.. prefer intel units, but all depends on your budget. From intel you would need at least Haswell i3, pentiums are to slow, such 2cores cpu cant handle most modern games with higher settings - and as always the best cost/effective choice are i5 4cores.
Maybe you should consider AMD FX cpu series (AM3 socket), if it would be compatible with your motherboard - any info?