You might be facing different issues all at once.
First, DiabloMiner does not have a version number as I don't officially release it. Just follow it via git, github, or subscribe to this thread.
Second, remove -f 240. It'll make your desktop lag, but you don't need nearly as much -f to stop that, AMD drivers are much better built than Nvidia's. -f 30 or -f 60 is what most people use on AMD hardware depending on taste.
Third, 290-310 seems to be about right for a 6870 at stock clocks. And try -v 2 over -v 2,1, sometimes its faster, sometimes its not for vliw5 hardware.
Fourth, makes sure you're running Catalyst 12.3 WITHOUT SDK 2.6, 12.3 ships with the OpenCL runtime and its newer than whats in SDK 2.6.
Thanks for the tips. I tried -f 60 with no noticeable lag, and a few extra Mhash/s. Now looking at more like 295-315! -v2,1 was faster for me, but the explanation does help.
Now, about the SDK thing. I just cleared my computer of all graphics drivers from Nvidia and then installed Catalyst 12.3... didn't do anything else. Should I have?