The new build performs sluggishly on my system.
Mac Pro 8-Core 2,88 Ghz
14GB ram
Logic 9
A single 64-Bit instance with 16 instruments loaded and a setting of 4 Threads will report a CPU usage between 30% and 40% when idle and will go above 50% when playing some instruments.
OS X Acitivity Monitor shows a CPU usage of about 182% when idle and approaches 300% when playing instruments. It also shows 27 threads.
The interface is very sluggish to the point, that it is a chore to drag instruments around.
The last stable version was a smoother interface experience for me.