Yep! They will work, although I'd make sure to set them both to the same clock settings once installed if they are different by default. I do not know whether non-reference models work well with reference models, but in theory it should all be the same thing.
Actually you can put cards with different VRAM together (6950 1gb and 2gb cards, 5870 1gb and 2gb, etc). The only thing is that you'll only have the smallest VRAM amount available, so 1gb. In CF and SLI, VRAM is not additive. Both cards will carry the same amount of VRAM with the same info, it's like a redundant array (RAID 1 HDDs for example).
I'm getting a lot of conflicting information on exactly what you can do with Crossfire. Mostly that you need your cards to be in the same range for them to work and I wanted a clarification before I made my purchase.
Currently I have a 5770, can I jump to a 6950 and Crossfire?? Should I just scrap my 5770 altogether and get a 6950 or should I crossfire two 5770?