Where are you measuring the keypress from? The nerve signal to your finger muscles?> Or the time the keycap hits bottom? What if the switch closes before the cap hits bottom: then we are getting a latency figure that looks better than it really is.

Nerve signals yes. I just try them side by side, usually running vim on both terminals and measuring how it feels. If you can feel difference, the latency is bad.

I've had a keyboard like that and with it, xterm (and nothing else) felt like it was displaying the characters even slightly before I had pressed them. It was a weird sensation (but good)