dont mid bull seems he has time to post just not to answer you.
With all the posts on these boards its easy to mis an existing one somtimes.
I think its a matter of preference and cost.
Some will argue the cheapest chip you can clock well is the way to go while others would say go for the 6850 and see how high you can go, I would look around at others overclocks and see whats been accomplished.
Those 6850's are going to be expensive, but I bet they drop the price on the 6800's when they come out, either way for my money I would go with the 6850, thats just me.
Lump