I done some testing now and this is what I found.
First, my motors are not optimal. Not well matched with drivers and voltage regulator. Too high inductance.
I got it as a "package" from Wantai motors, but obviously not a well composed package.
I have also changed to ballscrews.
* On one of the axis I was jumping between 3:1 and direct drive back and forth a couple of times and got consistent better performance with direct drive. (higher speed and higher acceleration without stalling)
I jog at around 1650mm/min and pretty high acceleration without stalling.
* I also tested microstepping and when going from 2 to 4 (or

motors stalled at VERY low speed and acceleration. So VERY much weaker.
Still not got my new voltage regulator (problem with shipping) so still not sure what I will be able to get out of my current setup without changing more components (e.g. motors that are better match to my drivers and available voltage regulator).
Still more test needed. So many permutations to test.....