4x Asus EAH6870 cards here
only using ATI control panel, GPU at 1015Mhz, mem at 1100 (in ATI control panel)
getting solid 305MH/s connected to btcguild.com
guiminer w/ phoenix flags -k phatk vectors bfi_int aggression=10 fastloop=false
no bios mods, overvolting, or reflashing
I am only able to get to 1000MHz clock using afterburner. even then, I can only hit 289Mh/s using OpenCL and 280Mh/s with Phoenix. On the machine I was testing I had XFX cards, which I have heard aren't fantastic.
I have a 4th card waiting to go in my machines, but can't get afterburner to work with 4 cards. Has the ATI control panel worked well for you in your quadfire setup? what version of windows are you running?
Also getting about 290mh/s at 1000mhz. Afterburner won't let it go higher than that. Runs at 60C though, so I'm happy.