The Asus Z97-A would have been the better option. Mainly because of the SLI support and the 4 phase doubled VRM. The C will still do the job though. As for the cpu, your overclock depends on the processor itself. You could get from 4.2-4.6....maybe higher....maybe lower. It is always somewhat of a crapshoot when it comes to overclocking. Some chips simply overclock better than others
what cooler are you using? Don't bother if using stock, If you want to overclock and have $40 handy look at getting a thermalright Macho 120 or CM hyper 212/X/EVO.