Now that I have my GTX 680 installed in my Mac Pro 5,1, I have a HD 5870 which isn't used. Provided that I use an external power supply for both cards, is it possible to install both these cards? That way I would have a boot screen again to boot older system versions etc. I don't think there is enough space between them to let cooling air in. Anyone tried this? Maybe a HD 5770 is a bit smaller? I know you can get a Mac Pro with two HD 5770 installed, so....?