I feel your pain. I got the notion that everyone was getting better performance out of stepper motors than me and I now have 3.4's which I drive at 220 Volts. Problem is they run hot and I don't trust them at full tilt which is strangely self defeating. You can't win. I keep thinking servo motors are the way to go but I have always been just one rebuild away from wonderful so I am not convinced. Do you really need mega speeds? What is the max delay, end to end on the table? Is it really a problem?

I suspect the reason we can't have nice stepper motors is that someone has decided they must all be 200 full steps per rev. I got a Roland mill which had 400 full step/rev motors and it is freakin' amazing.

You are blessed to have that quick tool release, but I am not so sure about driving the Z through the quill rack. I put a ball screw to drive the Z, a ball screw that has to be released every time I hammer out taper tooling. It's only one M8 cap head but I've already had to helicoil the thread.