Why not 75-80V drivers ...you'll get a decent improvement but it could have been a lot more with the higher voltage
i was tempted but my machine is a small dumpy little thing (500mmx400mm ish cut) iv taken the punt in hope of bringing the noise down a bit when running it for hours (in a shared house)
the steppers make more noise (when they hit the resonance) than the spindle cutting acetal at 300mm
iv got to tiptoe between noise and speed :)

I've cut acetal at 5m/min which isn't hanging about!
shit! id make millions if i could run at that :)