Well, well, well............I built two systems: Both motherboards are new Gigabyte S series with the same basic layouts (obvioulsy, the Northbridge chipsets are unique to each CPU manufacurer), dual 36 gig Western digitial raptors in RAID 0, Sound Blaster Audigy2 Z, 2 gigs of Corsair DDR2 800 EMS memory, Plextor DVD RW, Floppy, BFG 7950GT and Antec 500 WATT Samrtpower 2.0 PSU's; These systems were run at stock speeds and then oc's by 15% using the on-board Oc'd tweek program which auto adjusts all cpu, memory and PCI bridge voltages and frequencies. Here are the results:
Stock E6300: PcMark05 5816
Stock AM@ 4200+: Pcmark05 5882
Oc'd E6300: PcMark05 6110
Oc's AM2 4200+: PcMark05 6106
The one tell tale difference is that the E6300 never got above 38 degrees C. The AM2 ran Oc's at 49 Degree C.
Verdict = if you are buying an similarly priced low cost CPU's from either intel or AMD you will not be unhappy. They are both very close to being the same in performance.