In Live 9 during playback, the GUI responds more sluggishly. After stopping playback, the GUI responds normally.
I've been able to reproduce this in Live 9.1.2 32/64 bit. I am on a Retina Macbook Pro (Late 2013) running Mavericks 10.9.1
This is actually by design. On Retina displays, especially in Logic, the graphics were sometimes causing the audio to choke previously, so now I made sure they stay out of the way.
In a future release I would like to move to a completely OpenGL-based UI, which will be very speedy again.