So if im looking to buy one card at a time would it just be better to go with the 6850 and over clock. Plus wont the prices be droping soon because of the release of the 69XX cards??
An overclocked 6850 will get your performance up to 6870/5870 levels, BUT you need to be careful to get a model with a good cooler. Some 6850's can get VERY noisy when overclocked, particularly to the full out maxed clock speeds people keep talking about. Avoid the XFX and Sapphire models for example. Buying one 6850 will of course give you an upgrade path to Crossfire in the future.
Unfortunately, I'm not expecting prices to come down very much when the 6900 series is debuted. Apparently there is a MOSFET component that is shared by both models that is in short supply. As more of these are used for the 6900's, fewer will be available for the 6800's, therefore there might be a shortage of both cards.