That's what X38 & X48 is about!!! Higher fsb and stable o/c. I have tested three X38 boards (Abit IX38 QuadGT, Maximus Extreme, P5E3 WS Pro) and they all went pretty higher than 500 (520-565).
The one and only negative in those chips is the temperature, which is higher than P35. So if you want a highly overclocked system, you have to add a w/c system to your budget