That's harder to say, there aren't exactly a glut of PS/2 keyboards and mice these days or thorough testing data. And for good reason.
But the best keyboards these days approach around 0.8 ms: https://www.rtings.com/keyboard/reviews/corsair/k100-air
But the best keyboards these days approach around 0.8 ms: https://www.rtings.com/keyboard/reviews/corsair/k100-air
Also the field75 he mentioned in the OP does tie that keyboard's wired latency:
Best wireless mechanical is: https://www.rtings.com/keyboard/reviews/asus/rog-falchion-rx... (1.7ms @ 1kHz)
Best wired mechanical would be the Corsair Air 100 I linked at 0.8ms, tied with a Field75 which is also wired.
Isn't USB+2.4GHz modem by nature going to introduce more latency than just USB?
Is it directly connected to wireless somehow? Pcie card or something?