The multiplier of the processor affects the final overclockability by a grand magnitude of zero in most cases. A higher multiplier simply lets you use a lower FSB and thus a slower memory speed to reach your CPU speed goal. 3.2Ghz would max out the memory on an E6400, and the memory overclocks further than what is listen, especially when you start loosening the timings and raising the voltage. And yes, while a lot of E6700s manage to hit over 3.5Ghz, barely any of them are on air cooling. Remember kids, ever since the beginning, Conroes have not been expected to hit much over 3Ghz.
And lets not forget stability. Sadly though, it seems people have forgotten about it. WTF happened to the 24-hour Prime Stability tests? Its been reduced to around 2 hours of Prime or Orthos for the sake of higher speeds.