The processor landscape has been changed once more thanks to AMD's extremely aggressive price cuts. The Core 2 Duo E6300 is a better performer than the X2 3800+ but is also more expensive, thankfully for the E6300's sake it is also faster than the 4200+ and the 4600+ in some benchmarks. Overall the E6300 is a better buy, but at stock speeds the advantage isn't nearly as great as the faster Core 2 parts. In many benchmarks the X2 4200+ isn't that far off the E6300's performance, sometimes even outperforming it at virtually the same price. Overclocking changes everything though, as our 2.592GHz E6300 ended up faster than AMD's FX-62($695.99) in almost every single benchmark. If you're not an overclocker, then the Athlon 64 X2 4200+ looks to be a competitive alternative to the Core 2 E6300.
*** I added the $695.99 price tag for the FX-62, thats the current price for it VIA newegg.com
Remember NOW the E6300 and the 4200+ are the same $
The E6300 and E6400 can easily overclock to E6700 and Core 2 Extreme X6800 levels, though the smaller cache does limit performance a bit. That being said, our overclocked E6300 was able to equal and in all cases but one outperform AMD's Athlon 64 FX-62. In fact, in quite a few benchmarks, the overclocked E6300 is essentially out of reach of anything AMD can offer with their current K8 designs. At $182, the value here is tremendous, and if you're willing to overclock the benefits don't get any clearer than that.
See previous post. He's not an overclocker, so it's moot.