diff mem modules is this a problem?

mm ok,i have a 1GB kinston 750Mhz hyper x module and my dad thought hell do nice and buy me another so he bought a Corsair XMS 1GB DDR 667 module, is this an big issue, my pc runs fine with them everything stable, cpu-z says my mem runs at 333.33 mhz and the timing are all the same,seems like the pc is o/c the 667 to ddr 750mhz speeds(333.33) or that was the speed with only the kingston..benchmarks didnt improve from 1gb to 2gb.