Low performance with a lot of edits

(I also sent a support request on this issue)

Im running a Mac Pro 3.1 - 8x3Ghz Xeon 10GB Ram, SSD for OSX and 1TB WD hdd for projects. Radeon 7970 3Gb Gfx card.

the project is clean, all unused media removed and deleted from trash.

the issue:
when editing drums, lets say 16 tracks, everything chopped up with a lot of events and autofades when zoomed out so the screen renders all the events the performance is very low, the zoom in/out lags.

it is not OS related, the same happens on another machine with the somewhat same specs and running OSX 10.9

when zoomed all the way in and working with cut and so it works great.

so the question:
is this a cubase problem, or my hardware performance?
my machine should be more than powerfull

I dont get at all why this is happening, can you please shed some light on this

Thanks in advanced