IIRC the e6850 runs quite cool and was (is) a decent power-miser. eWiz has e6850 OEMs for $129 (I almost snagged one but decided my $129 was better spent on a Phenom 810
)
I think what makes them 'equal' is the e8200 has more L2 cache and SSE4 ... but it only has an *8* cpu multiplier Either one will work just dandy.
As gkay09 noted DDR2 800 will work fine. With the e6850 your RAMs will be 1:1 at 3.6GHz (400MHz x 9) and 3.2GHz with the e8200 (400MHz x 8).
Simply because of the price difference I'd go for the eWiz OEM e6850 --- especially if you already have a cooler (or snag the Phenom 810 early tomorrow when they restock if you are going to buy a mobo anyway).