Had some time and did some testing with these Tahiti GPU.

Basically XMR-Stak seems to work. The version I used is XMR Aeon Stak 2.5.2 and I found the link in Mattthev signature.

If you got the 7970/280X use intensity 920 and you should get at least 500Hs and up to 550Hs depending on how high your core/engine clock is set. At 1000/1500 you should get close to 500Hs and the GPU shouldn't consume much electricity, around 130Watts or so.

With 7950 with 28 Compute units you will need to lower the intensity a little bit and your speed will be slightly lower.

If you are getting incorrect shares, you will need to lower your memory clock.

Putting these numbers into What to mine with 10 cent power results in a total net profit of nothing. So if you are a die hard hodler or got free or cheaper power, you can mine XMR but for most i think it's time to pack up these GPUs.