Electronics for New Machine + Chinese Spindle + VFD

[mturneruk]

I was increasing my acceleration and velocity as I went along. Bit at a time.
What i noticed was that the Z axis was the limiting factor, so i increased it, and then obviously my job completed faster, but I felt sorry for my machine. Everything was very warm. Spindle, steppers etc.
Not boiling though, but very warm.

Also I only have one 3mm ball nose bit and i didn't want to break it. I roughed with a 6mm ball 2.5mm stepover, 5mm DOC and then finished with a 3mm ball with a step over of 0.75mm.
Forgetting the design I did, what is the optimum tool size / Stepover for this kind of thing?

Something tells me it's better to design something that allows you to use a bigger tool.