Perfectly possible.
I used to run a 5870, 6970, 7850 and 7950 all in one machine.
Perfect, just what I needed to know, thanks
EDIT: On a side note, what setup would be best for my air flow / heat management?
Im thinking the following, if I plug one of my 7950's into a x1 -> x16 riser - this shouldn't affect mining afaik?
https://i.imgur.com/y1MVq4z.jpg