Yeah I'm running GUI Miner on my HD 6970. I'm going to buy a couple of HD 5830s for mining.
Does anyone know if running in a 4x slot affects a cards hash rate?
No effect. BTC mining needs very little bandwidth. Much less than even a 1x slot delivers. Many, many people over on the bitcoin forums use 1x PCI-E extender cables to run the cards off the 1x slots.