Best settings for my new setup?

[Shonumi]

Are you playing by yourself or with other human players? The more people you play with in multiplayer games, the more demanding it will be on your computer. If it's just you by yourself and you notice that you get slowdowns at specific parts of the track (when you're racing around, you might not hit the same spot twice, hence a problem area may look random) try scaling back some of the graphical enhancements.

Also, see if Lock Threads to Cores helps at all.