I have a few rigs running 4x7950 (msi) and get around 1900h/s, 475h/s per card with 1120/1250. I also have a few rigs running 6x290 (sapphire) with 1100/1300 getting around 3900h/s, 650h/s per card.
I have tried upping memory but see very little changes in speed compared to say scrypt mining so performance/power suits myself best with those clocks.
How do you get 650 h/s per card. I've got only 385 h/s for 290...
4x7950 @ 1120/1250
6x290 @ 1100/1300
3.1 miner was very stable for myself, have updated them to 3.4 miner and it looks as stable but with the added bonus of going back to main pool. All rigs are running windows 7x64, 13.12 cats, 8GB RAM and 16GB pagefile. For the 6 card rigs I'm using the 13.12 mod https://litecointalk.org/index.php?topic=11761.0, that trick has also worked on one of my rigs with 4x7950 and 1x 280x.
I was running one of my rigs with an 8GB pagefile for a while without realising, changed it to 16GB and got the same hashrate, so not sure what that was about.