Well at least we know what was causing the slowdown.Unfortunately I've had to put 7.7 back on - rolling back to 7.5.5 had broken Safari and iTunes. When I do a fresh install will be sticking to the older version though.
I wonder how many other apps and UI features are held back a little by 7.7?
I notice iTunes requires QT 7.6 or better, maybe there is a sweet spot, something less then 7.7.