With the shiney new kentsfields out, there isn't much point in the X6800. If you're rich enough for the X6800, just go all the way and get the best thing out, the quad core Kentsfield.
that said I'd just consider Ocing with a scythe ninja. I oc off AIR and my computer runs all the time. While yes every processor is different, the point is you won't know until you try.
Opteron 175 + Scythe Infinity
2 gigs corsair XMS DDR 400
XFX geforce 6800 XT
30G Maxtor + 250G Maxtor
"Let's face it, we're not changing the world. We're building a product that helps people buy more crap - and watch porn." -- Seagate CEO Bill Watkins