Like Gunja : very significant FPS drop not only on S/F straight but in some other places, there are far too much objects around the track, this is good for screenshot, replay and making video, but it's bad for just driving IMHO (unless cruising at 10 km/h, I guess we can't notice that much all the stuff around).
Perhaps replacing complex objects with only faked ones (a simple facade, like in movie decors :) one quad and a texture instead of a lot more, for trucks for instance), in a lighter/alternate version of the track would be great.
FYI I have an Asus ROG G75JH-T4024H with a GeForce GTX 780M, an i7-4700HQ, 32 GB ram with Win7 SP1. It's the only track I've noticed such big FPS drop.