Multiple but different AMD cards - Any experience?

One of my dual 5770 cards in my Hackintosh needs replacing. I have dual 5770's that drives three monitors.

Whilst I can simply replace the 5770 with another 5770, I wondered if I should take the opportunity to upgrade the failing cards and thought about a 7970 or similar.

I was wondering if anybody had ever run a different AMD card with a 5770. I know that the nVidia cards and the AMD cards do not play well together, benchmarked that setup and laughed but I can't seem to find anybody who has run multiple AMD cards and FCP X.

The reason for not moving straight to a single 7970 is that I like the three monitors and I can't go to dual 7970's as my PSU won't support the power drawer. Additional PSU plus dual 7970's is expensive

So, anybody had any experience in say a 5770 AND a 7970? I've no doubt it will work, but will it work effectively?

Thanks for reading.

Rob.

FCPX and Motion can only use the resources of a second GPU if both are the same. Aside from that, not sure there's any other reason to not use two non-matching cards.