You're right about not needing the new PSU until you're ready to CF.
A good MB that overclocks well and supports CF in 8x/8x mode is the GIGABYTE GA-Z77X-UD3H for about $150 at Newegg. http://www.newegg.com/Product/Product.aspx?Item=N82E16813128544
As ofr CFiring the 6950, it doesn't have to be the same brand, just the same model.
As for the cooler, go for the CoolerMaster Hyper 212 EVO. It's got a good reputation for a reason.