Both the HCG 520m and the S12II 520w are rated very high. I'd pick the HCG 520M due to modular cables, because you'd want to have as much free space as available in an ITX case anyway.
Anyway if you want to OC with your ITX system then Haswell CPUs aren't good choice, due to the large amount of heat they produce. Right now Asrock Z87E ITX would be the only ITX board that's capable of OC-ing a Haswell CPU. If you want to OC but want to keep the cost low also then you'd better grab an Ivy bridge combo instead, like i5 3570k + ASRock Z77E-ITX.