I, too, have come to point where if this is not completely fixed in C9 I will need to go back to Pro Tools, which would be SUCH A BUMMER because I left Pro Tools for Cubase a few months ago!!! The slowness of the C8.5 GUI compared to Pro Tools on my Mac is unbearable though, so the tradeoff is not worth it to me. It’s such a damn shame that I would have to abandon Cubase for this reason alone (and one other big one, the CPU efficiency), but it’s such a major, major, major thing when I work on large projects back-to-back for a living every day and need the GUI speed that I get with every other DAW I’ve used or tried on my Mac. 
It’s so sad for me to already turn into one of the so-called whiners here, but this is the reality of working with Cubase on a Mac right now.
Fingers crossed for a fix for this (and the Cpu efficiency) in C9!