This
At 38hz the input lag is acceptable. If there was a brute force way to disable the scaler we'd have good looking 4k res w/ tolerable lag.
As has been mentioned many moons ago in this thread, to get native 4k resolution the input board feeds 120hz 1080p to do 4k 30hz (sending 4 1080p frames per frame.) I think this adds a lot of the input lag.
It also forces it to run at 30hz 4k, and it simply cannot without a lot more modwork work at higher resolutions (31hz even frame skips.)
I disabled via a firmware mod the 31hz scaler that turns on and put it at 38hz, it does not improve input lag and simply adds more frame skipping.