Slightly related - when I run a cheap command in xterm (bitmap fonts) on X11 with a plain and fast window manager (no compositing) I often have this weird sensation that the output appears before I've actually hit the return key.

It might be just due to the surprise given how much software has bad latencies, but it might also be that the processing of the sensoral inputs from my fingers hitting the key takes longer than the visual response from something appearing on the screen.