strictly depends on how much of an OC you're looking at. i'll mention again; the 3570K tends to overheat when you raise the voltage, usually around 4.2-4.3ghz. this should give you a performance close to or even better than a 2500K OCed at 4.5ghz. consider as well that you said you planned to OC this moderately, and these OC's i'm mentioning are somewhat beyond moderate already. at the same clock speeds, say 4.0ghz, the 3570K will win in most, if not all, cases.
if you actually have plans to OC beyond 4.5ghz and get a custom water loop, then a 2500K isn't so bad if you're really concern with heat. below that, and on air cooling, i highly recommend the 3570K if money isn't a big concern.