Hi,
I've found that high speed low torque spindles are very poor choices for milling steel.

You can engrave, light finish cut with small diameter (3mm or less) endmills but that's it.

I made a second spindle especially for steel. I used a 1.8kW Allen Bradley servo (3500rpm/6.2Nm cont) and
cylindrical ER25 toolholder and P4 angular contact bearings. Just the 'bees knees' in steel.

The majority of time (90%) I use my highspeed spindle and only swap over to the 'grunter' when I need it.

Where-abouts in NZ? I'm just out of Christchurch.

Craig