I hope this may be useful. It's a screenshot at the end of the worst 4 seconds of the replay from the race, when my fps drop in the 60s. As you can see, CPU is running very well, with no thread above 50% occupancy. You can also see that the GPU is also well below 100%. In fact, it drops (!!!) when things go bad (just before the screenshot). So something is not feeding the GPU fast enough... no?