Let The Fun Begain, New build on the Table.

[Jonathan]

I have just done a member search on ebay but aliexpress have not been trading in the last 12 month
But I will take your advice and order 3.1Nm stepper and four separate drivers.

By aliexpress I didn't mean the eBay seller, I was referring to the website:
Cheap CNC! Wantai 4 PCS Stepper Motor Driver DQ860MA 80V 7.8A 256micro CNC Router Mill Cut Engraving Grind Foam Embroidery-in Motor Driver from Industry & Business on Aliexpress.com

Jonathan also mentioned aiming for a higher design speed to give headroom on the constant cutting speed but this head room is not wasted as you can have fast rapids when moving between cuts (subject to mass/inertia limitations of course) cut at 5m/min move at 10m/min

True, but it's worth noting that a high rapid speed (up to a point) doesn't make much difference to the overall job time compared to a lower speed - 5m/min vs 10m/min is a good example. Often you'll find even doubling the rapid speed will only reduce the overall time by a few percent. This is because in general the machine is moving much slower and in many directions with a finite acceleration. The acceleration often limits how fast the machine will go, since every time it moves to a different position, or changes direction, at least one axis has to accelerate (or decelerate) and the speed is often limited by this. One good example is detailed engraving - the individual moves are very short, so each axis is almost constantly accelerating (and decelerating) whilst cutting, and in addition the rapid moves will generally be short so the machine may not get up to the full rapid speed, hence the speed is likely to be limited by the available acceleration.
Similarly, if the G-code is well written then the proportion of rapid moves will be quite small (clearly there are exceptions). Suppose the rapid moves comprise 10% of the total time taken for the job. Here, doubling the rapid speed will only take 5% off the overall job time.

Clearly there are exceptions - if the rapid speed is limiting how fast you can cut, then having more speed (so long as the acceleration is sufficient to use it) will decrease the machining time noticeably. An example of this is surfacing an MDF bed, where cutting at 10m/min would be perfectly reasonable (I do it)...but then how often do you need to surface the bed?

Often it's a compromise between maximising speed and acelleration, since increasing either requires more power and the motors only deliver a finite amount of power. With pulleys you can adjust the ratio to optimise for better speed or acceleration, but in the end you still need motors with enough power - hence my suggestion to get the 3.1Nm motors as their power output is plenty and they're better priced than virtually all other realistic options.