I actually did this with the load cell recently. You can pass the PROBE_SPEED=5 argument to QUAD_GANTRY_LEVEL to override the probing speed.
There is a lot to be said for the idea that faster speeds shake the printer and reduce accuracy. A better idea is to use lower speeds but for much shorter distances for the same speedup. e.g. my sample_retract_distance is 0.3mm and my standard probing speed is 2mm/s.
I have a thread about making the horizontal_move_z a relative move so it can adapt to taco bed shapes. IMHO, the focus on fast probing exists largely because the current horizontal_move_z behavior in klipper is bad for automated probes.