i'de say the e6600 if you plan on overclocking. on air cooling it easily will run at 3ghz, and 3.4-3.6 is usually do-able on water cooling. i have mine running at 3ghz and i must say im overly impressed with this systems performance.
They are all excellent overclockers, although the E6300/E6320 are the worst. I just built my brother a computer, and I gave him an E4400 since it has the highest multiplier of any of processors on that list (10x), and hence it is the easiest to overclock.
@SealBoy, E6300 are the worst for overlocking!?, so how comes Legion and Toms both wrote articles saying the E6300 is the best choice for overclocking?
It's not the worst per se, it's just the hardest to overclock due to the low 7x multiplier, which results in very high FSB and RAM speeds to get 3.5GHz. You need an excellent overclocking mobo + DDR2-1000 capable RAM.
With the E4300 you can realistically get 3GHz with a cheap mobo and DDR2-667.
a gigabyte DS3 is $99, and I've built 3 core 2 duo (e6300) systems running generic DDR2-800, all at 3.5ghz (memory at 1000mhz) as per that legion article and they all work flawlessly
DDR2-800 is what, $10 more per GB than 667? more than worth it IMO
the extra for the E63 gives you a whole lot more bang for your buck than an E4xxx, but more money on the proc gives you diminishing returns in terms of overclocking as most E6's won't go much above 3.5ghz anyway
E4300 is one of the best out there and excellent of overclocking for it starts with low FSB. You can get a 2x1Gb DDR2-1066 for $125 and used that for overclocking. Depending on your components and cooling you can overclocking the E4300 upwards over to 3Gb no problem. This will give the Core 2 Extreme a run for it's money. But if you can you should go ahead and choose quad core as it could last you more than the dual cores. It's not going to be long enough before the Dual cores gets phase out with the quad cores next year and more applications and DX10 games will be taking advantage and every single ounce of the cpu. Take Crysis for example, it is optimized for quad cores and soon all good games will follow. But for now I guess the E4300 will do just fine until next year. So I highly suggest for you to get that E4300 and save up the rest for the quad core upgrade.
I got the e4400 because it is a joke to OC due to the low FSB and high CPU multiplier. It practically OCs itself.
I've never done an OC before, but I got to 2.7 GHz on my first try, spending only 15 minutes doing it, and it booted on the first try and it is totally stable. I think I'll do a 3 GHz OC this weekend (on stock cooling!)
At 2.7 GHZ or 3 GHz it is fast enough to run anything out there now, and I intend to buy the Penryn quadcore (yorkfield) late next year when the prices come down.