I also am experiencing low fps when I have DB window up with D3 window. If I minimize DB fps goes back to normal. All drivers are updated. I've removed and reinstalled DB three times trying to resolve this issue along with other issues like being disconnected. I have just learned to start DB, minimize it then let it run.
Hey Tony, quick question... could DemonBuddy be conflicting with any of my PC hardware? In the meantime, I'm gonna re-install Diablo 3 and do another fresh install of DemonBuddy to see if any of that fixes my FPS issues.