Multi-core rendering is enabled (that setting is forced on by Chris' maxframes). Also my hl2.exe core affinity is set for both cores at "normal" priority. I've read from multiple threads that setting it to a higher priority could cause issues.
Since creating the thread I've deleted my Team Fortress 2 folder and am still getting the same issue.
#2
If you have an uncapped fps it's not going to remain steady. If you're using maxframes make sure you set the launch options so that you're running -dxlevel 81 on your first launch. Make sure you don't have a lot of background applications and use task manager to filter processes by cpu usage. Ideally, the only % of cpu usage should be coming from hl2.exe. Disable aero if you're running Windows 7 (I forgot to add this in the OP, but I'm running Win7 and have aero disabled) for a few more fps.