http://www.xbitlabs.com/articles/cpu/display/intel-wolfdale.html Comparison of performance. Definitely a good read!
Took the E8400 up to 4.2 with only a single click up on the voltage (425, if i remember right) was solid. Water cooled it is. Took it down to 3.6 with (410) and NO voltage increase to the CPU., runs solid as a rock and according to the temp utility BELOW 100f Quite a killer chip for the money. I paid $242 when shipping was included.