What I think I have understood so far

[SeraphimLeftNut]

In order to minimize input lag you have to minimize prerendered frames (gpu control panel)
In order to have smooth gameplay you have to have high fps: no bottle necks in cpu or gpu and a low sc_frametimeclamp value (default 10 ms, up to 100 fps)

Setting prerendered frames to be capped at 1 puts a lot of strain on cpu (unless you have vsync on or a frame rate limiter on, both of which have caused a lot of problems for me)

If CPU is maxed out the GPU likes to go to sleep (turning down the core clock) in order to avoid this you have to set power management mode to prefer high performance in the control panel. (I also have to trick my gpu into not dropping the clock speed by doing other things, but you can explore this yourself, msi afterburner is great for keeping track of what your gpu and cpu are doing)

The bottom line:

Do everything possible to make rendering easy for the cpu, because it is quite easy to max it out (rendering thread, not the sim thread)
Taking suggestions on how to do that here