I'm using a Dell Studio Hybrid with a T8100 (mobile Penryn) and it averages about 80% CPU utilization with CoreAVC 1.9, although it will occasionally spike to 95+% (like maybe once every 15-20 seconds) although won't stutter when this occurs. This is with 1080p h264. With 720p it settles around 50-70% cpu utilization.
My question is, do you currently have that computer, or are you planning to pick that up?