I did the flight test over Barcelona again, but now with Dx11 and I got about a 5-10 FPS bump on average but about the same amount of sudden stutters/dips in framrate. Couldn’t discern any graphics quality changes to speak of.
Tomorrow I get my new SSD and will do a clean install (best way of removing the current one best - Revo Uninstaller or similar app?) on it and report back if it further improves performance. I will start with the settings I have now for comparison.