if overclocking isn't an option, the 4800+ is faster... the core 2 duo performs about 25% better in most benchmarks, and even less than 25% in some (per clock of course)
so, 1.86ghz *1.25 = 2.325ghz... the 4800+ is at 2.4ghz.
its not exact, but its probably the best thing youve got to go on. its not perfect either, because sometimes the athlon 64 does actually perform the same as the core 2 duo (per clock) in some apps...
either proc is great, and i'd probably choose the e6300 just because it runs so cool anyways...
i mean people dont have fans on them a lot of the time, just because it doesnt even need it.