Hey Beezer,
I was one of those having some frame rate weirdness. I never really figured it out.
Before this started I did upgrade to CSP 1.62 and tried the DXGI fiip mode, but didn't notice any difference, so I turned it off. I also added an app. I later noticed frame rate had taken a dump. I reinstalled CSP, SOL, got rid of all my apps, but nothing seemed to change. I think it was Masscot who mentioned possible memory leaks, but in monitoring, everything looked okay. It got me thinking though, so I started examining my Windows install. In the updates page I found a failed update attempt, so I let it update again and restarted.
I was working on ai, so I decided to give up on figuring out the problem for the time being. I ran a bunch of short test races. Seemed like it was same situation. Good at first then in subsequent races, the frame rate dropped. After several, I noticed frame rate started coming back incrementally, until it was back to normal. Weird.
It's been back to normal since, and I went back to 1.62 without frame rate issues. I also added that app I was trying to install. I did eventually go back to 1.60 as it seems like the new VRC update to the Formula NA's don't like it for some reason. Sometimes I would get 15 fps with those cars and 1.62. Going back to 1.60 and they seem fine.
Hope you get it solved.