I've noticed there seem to be alot of lag threads for the various Penumbra and I recently solved the lag problem I was having in Overture. It was lagging no matter what settings I used but using this list here:
http://www.sysinfo.org/startuplist.php
And disabling unneccessary startup processes in MSCONFIG fixed it. If you don't know how to get into MSCONFIG just go
Start->Run and type in MSCONFIG. The startup tab is the one you want and just work through the list, using that site I linked to, to find which processes aren't needed. You will most likely find you have some superfluous mouse/keyboard/soundcard processes for functionality you never use.
Hope this helps some people.