I originally noticed this on the SEM but found it to be true with the Wurlitzer as well.
When playing notes on a midi controller with the GUI open in a DAW (read VST not standalone)
it would cause the CPU usage in the DAW to spike
It only happened if the GUI was open.
I am using windows 7 64 bit SP1
my configuration (was) to have windows desktop Aero effects turned off. When I turned Aero back on (hence I believe utilizing the dedicated graphic card GPU) the problem went away.
Not a fix by any means and might not be applicable to anyone else having the problem, but Im sure there are a few people out there that have the issue and might still be struggling to find the solution.. so hope this might help someone else.