onMouseMove is normally delivered at the video frame rate, 60 fps. The OP's benchmark shows it can deliver around 60M signals per second, so it uses about 1/1000000 of the CPU time. Seems tolerable.
Even if it was delivered at the polling rate, that should never be higher than 1kHz (otherwise you deserve whatever performance issues you get). A virtual function call is 15ns conservatively, so say a signal is 150ns. 1000x is <150us of wasted time, well below observable overhead in any human-centric application.