I started mining in earnest last week with two cheap Ubuntu 10.10 machines, one equipped with a Radeon 5870 and one with a 6870, both running Diablo.
I'm getting 290M on the 5870 and about 220 on the 6870. According to the ratings at http://pastebin.com/AvymGnMJ
this is almost 10% less than they should be capable of.
I have all of the compiz effects turned off and as little screen activity as possible going on (blank screen-saver). The only flag I have set is a worksize of 128. I've tried 64 and 256 but it didn't seem to make much difference. I tried the v flag once but it didn't seemed to be supported (threw an error of some kind).
Any suggestions/tips for how to squeeze more out of them?