Thanks for the upload mezza550, I've followed the exact same procedure as you've stated here and can report very similar results for my 3x 11221-00-20G's -they hover around 700-707kh/s. My setup is pretty much the Cryptobadger rig: http://www.cryptobadger.com/2013/04/build-a-litecoin-mining-rig-hardware/

Now I'm wondering if I can get a few more khash out of them, It would be nice to end up somewhere around 740. What I'm going to try in order of importance:

1. Fine tuning the overclock.
Right now they are all on --gpu-engine 1065 --gpu-memclock 1500, probably can adjust the sweet spot further for individual cards.
Q: No performance gain by overclocking memory on 280X?

2. Going from cgminer to sgminer and try out a few other kernels.

3. Look at other Catalyst/SDK version combinations.
Right now I'm at Catalyst 13.11 beta 9/APP ADK 2.7.

4. BAMT
I tried ubuntu, went half insane trying to do the simples things in a broken UI, went back to windows. A pre-configured mining-specific Linux enviroment like BAMT should be better optimized and thus give slightly higher hashrate. Problem with support for Wi-Fi cards though.

5. Pray
The patron saint of miners is Saint Barbara, she might bless me with a few extra khashes
http://en.wikipedia.org/wiki/Saint_Barbara