Hi Jonathan

Thanks for that. I have a big spreadsheet of my configuration - here is a cut and paste of the motor data:

Axis Model Configuration V A Nm mH
X1 M60STH88-3008DF Bipolar Series 5.46 2.1 3 12.8
X2 M60STH88-3008DF Bipolar Series 5.46 2.1 3 12.8
Y* SY60STH86-3008BF Bipolar Series 5.46 2.1 3 12.8
Z** ? Bipolar parallel 1.8

* this is the new motor but to keep the X axis motors the same the old Y motor will go on the X2 axis.
** can't remember why I bought the Z axis motor at 1.8Nm but it's been working fine for years.

I'll look into the higher voltage drivers and weigh it all up . . . .