I have the E4300, I have all voltages running at stock on an ASRock 4CoreDual VSTA motherboard, see below for specs. I am currently running at 266FSB for 2400MHz. Best overclock of any processor I ever had... totally stable...
I would start by using default voltages, overclock in stages, I started at stock speed 1800 (200FSB) , then 222MHz, then 233, then 266. Have not had to modify any voltage settings as of yet. I would not bump the voltages up until you start failing either CPU or memory benchmarks, bump up CPU voltage if CPU benchmarks are a problem, memory voltage if only memory benchmarks are a problem...
I am still using the stock Intel cooler, but may try for 300 FSB after I get something better like a Thermaltake or Zalman cooler... but so far I am pretty impressed with the E4300
Its my first Intel CPU since the 386Sx days. (Prehistoric)...