Yep, we got a bunch of Gigabyte 280x. A little VBE7 to undervolt the BIOS, and they're hashing in Linux and Windows just fine @ 725Kh/s. Very quiet, and cool.
What voltage do you use?
725Kh/s @ 1025/1500 @ 1.019V
What's the advantage of using VBE7 instead of Trixx or Afterburner?
1.019V is really low. I can't go lower than 1.100V using Trixx.
Are the voltages that are displayed in Trixx or Afterburner different form the "real" voltages?
The advantage is that I'm using Linux. I can't use Trixx or AB. Also, because it's hard-coded into the BIOS, it will ALWAYS run at that voltage, without having to run another piece of software that adds another point of failure. KISS.
ALso, 1.019 is really low. But that's what I set VBE7 to, that's what cgminer reports, and I cut 200W off at the wall or the 5 card rig.
Try VBE7, and make sure to keep a backup of the original BIOS. If you can go lower than 1.1V, great! You can go down in steps: 1.09, 1.07, 1.05, 1.01, etc. If it doesn't work for you, then flash the stock back and keep using TRIXX.