I got the single-core CPU client set up since my last post. I may look into the SMP one as well - I think that's what I tried to set up last time. Still not sure if the single core one is working. It was doing work for 5 minutes or so but just now decided to get a different work packet instead.
As for Civ... my Civ3 games would take forever with limited CPU power (gigantic maps). It will depend on how good the SMP client is at powering down. Although it looks like temperatures may be an issue first.
The GPU is estimated at 611 PPD by FahMon. Does this sound reasonable for an 8600M GT? I've got other drivers downloading to try if it's unusually low.
edit:

97ºC on the CPU. That's a bit too high for me. Don't think I want to leave the CPU one on overnight quite yet if it's running that hot with just the single-threaded one and not much else taxing the CPU. Might have to go just GPU. It maxed at 77ºС by itself, which is acceptable.