Something seems to have changed ... Kaffeine now produces a correct image for HD playback with full resolution. SD still seems to suffer from a reduced resolution; better quality in vlc. I'll have to find out whether hardware acceleration is now used or not. However, I cannot compare the current CPU loads to the numbers shown here, since I upgraded my system a short while ago (new CPU and new graphics card). So this is not really an issue for my system anymore, regardless whether HW accel is used or not. If you like we can close this ticket.