They're both 3.0GHz, but one has 50% more cache, uses way less power, and can OC way higher.
At newegg, the e6850 is 275, while the e8400 is 240 (OOS, but you can find it elsewhere for cheaper anyway).
Source: http://www.xbitlabs.com/articl...ay/intel-wolfdale.html
It seems like...