I have an E4300 that runs pretty solid at 3.2GHz with only a minor voltage increase. The earlier E4300's like Rodney has take quite a bit of voltage in order to get a good OC and I believe that increased voltages, especially over 1.5v is extremely dangerous on a 65nm CPU. I have taken mine up to 1.425, but I won't run that for prolonged periods.
If you grab an E4300 - you can easily run it at 1066 x 9 = 2.4Ghz - most of the time at stock voltage and everything. If this is possible, you won't cause any undue damage to your CPU - and you get 600MHz free performance (x2 for dual core).