Steps per unit daft question

[JAZZCNC]

I can't imagine how hard it is for our yankee chums working all this out in Inches

No harder just decimal point is in different place.!!

I went with 10x steps for the X & Y - and 4x steps for the Z as the motor would stop rotating at higher speed using 10x - my thinking behind this is that I get more torque the lower the steps....... Correct me if I'm wrong there though please!!!

Well your sort of correct but like most things in CNC it's not that simple.!!
Resonance is big factor in stepper performance and lower micro stepping often make the motors run in area that they get affected by resonance. This cripples the performance.
Jim mentioned it briefly but playing with micro stepping can drasticly increase performance. Every machine resonates different so there's no one setting that suits all machines. ~However rule of Thumb is that higher MS runs smoother but at the cost of stress on the pulse engine. Basicly many more pulses are needed. So if your using the Parallel port some times running high MS can tax the parallel port which struggle to cope with supplying consistant train of pulses. This degrades the quality and frequency and all sorts of strange things can happen. Things from missed steps to poor performance or stalling motors.

That's why External motion controllers are much prefered if running machines at higher feeds. like routers. Small machines like mills etc can get away with using PP and lower MS because they rarely run in Mid band or higher speeds which is where steppers/drives get affected most.