I'm using one 6870 and one 5830 with guiminer and phoenix.
Using the phoenix miner for one gpu works fine, but when I start the second miner, the mhash rate drops about 100% using a second phoenix miner, or about 30% using the normal bicoin miner.
http://img7.imagebanana.com/img/b5miko66/fdfdf.JPGIs there a way to get this working?