My mouse also lags when a few apps are open in Ubuntu, can't figure out which one is causing it. (But I know the wallpaper app, Variety, definitely made it worse)
I can't test in XOrg because it doesn't detect my monitors correctly.
However a week ago before I had switched from Kubuntu to Ubuntu, KDE on Xorg had no mouse lag or problems at all.
My mouse also lags when a few apps are open in Ubuntu, can't figure out which one is causing it. (But I know the wallpaper app, Variety, definitely made it worse)
I can't test in XOrg because it doesn't detect my monitors correctly.
However a week ago before I had switched from Kubuntu to Ubuntu, KDE on Xorg had no mouse lag or problems at all.