Hm, what input lag? There's none whatsoever with my setup (well, probably measurable, but nothing that can be felt or differs from LFS).
It must be frustrating not to be able to use the markets best sim at the moment (just my opinion). LFS is great too (especially netcode), but it falls behind in many areas now. Hopefully, Scawen has the time and motivation to push LFS back to the throne (considering family/house/hobbies...).
Still use LFS, but if I'm going to Blackwood, it's with the BMW E30 in AC.
You could leave Vsync on, but cap the framerate at 59 or 60hz. This will impede vsync from buffering another frame before displaying the image on screen (it cuts 16.6ms of latency). It becomes very acceptable