Have seen no reports, but I bet they will be the best overclockers of the e4xxx series. I had some doubts whether the e4500 would be a better overclocker than the e4300 or e4400. Though early reports were iffy, the M0 stepping processors have proved to be better overclockers than the L2 stepping ones.
Statistically, each successive generation (e4300->e4400->e4500) has overclocked better than the last. Individual chips vary and there are exceptions. I have an e4500 that I am quite happy with. I'm running it at "only" 3.4Ghz, but I have had it as high as 3.8Ghz and still don't know yet what the upper limit is. Realistically I have to run it slower because of cooling issues, but that's a nice problem to have. Still working on that one.