I just bought a new graphics card and was wondering if I'd be able to use it with my old one, or if I just need to just use one. My old card is a XFX Core Edition FX-785A-CNL4 Radeon HD 7850 and the new one is a Sapphire Radeon VAPOR-X R9 270 . They both have Crossfire support, as does my Sabertooth 990FX board. I know mixing and matching RAM is a giant no-no, but I'm not sure about GPUs. Any advice or recommendations would be greatly appreciated, thanks!
Well there are some cases you can Crossfire two different AMD graphic cards but they require the same GPU. In your case you are not able to Crossfire those two graphics cards. There is also a table where you can look up to see which cards are compatible with each other.
No, I don't think you can mix GPUs if they are not in the same series.
But maybe some can as they essentially have the same GPU. See more here.