Using Windows Vista the first thing I noticed was that dragging a window causes a replicate display:
Second thing I noticed was a slight border display error with what is a guistyle/.wba which wasn't occurring with V5:
I'm not really able to test further very easily as it runs at an extremely slow speed, my best guess would be that this is the result of not currently having the bitmap fonts option as script times were not excessive, better than on V5 infact:
Checking CPU usage within task manager seemed good too, although opening task manager prevented me from being able to re-open the client having minimized it.