I am going to talk you the experience I had today. I was participating in a 6 hours race which had 50 cars in Road Atlanta. The mod used was GT3 from Apex. Well... first hour was a disaster because I was having a lot of lags + spikes all the time. It was undriveable and graphic settings were in lowest because I had the same problems in the test races the organization did. All of this happened in DX11. I am normally able to run Full Graphics in DX9 with no problems. After the first hour having these problems, I desperately gave the car to a team mate and tried comming back to DX9. My surprise was that all my problems were fixed and I could keep racing till the end with 0 lags and spikes, 0 problems. This is a serious problem, both builds (DX9 and DX11) were with lowest settings the game allows me and with edited player.json to allow less headlights and less meters in the mirrors view but the difference was that DX9 was running perfect and DX11 wasn't. I hope you fix these problems in the near future because they are obvious DX11 problems. I hope this experience will make people and developers to think about this. See you.