Very interesting article, thanks. I'll leave it set to Supported-Supported to be on the safe side.

Should "Set Phase Current" be the rated current of the stepper? I'm sure that's going to be the winner of stupid question of the month :-).

I couldn't help feeling I was drowning in a sea of numbers comparing the various options so I put together a little table (hopefully others might find this useful as a starting point). I threw in a single calculation for a shorter X-Axis as well just to see how much of an effect that had.
# Ballscrew Length
mm
 Stepper Nema Supplier Price Max Speed
mm/min
 Limiting Factor
1 1610 1800 60BYG301B 23 CNC4YOU £25.99 3500 Critical Speed
2 1610 1600 60BYG301B 23 CNC4YOU £25.99 4500 Critical Speed
3 1610 1800 60BYGH401-03 23 CNC4YOU £38.99 3500 Critical Speed
4 2510 1800 60BYGH401-03 23 CNC4YOU £38.99 1900 Torque
5 2510 1800 86HS115-4208 34 CNC4YOU £79.99 4000 Torque
6 1610 1800 SY57STH76-3008B 23 Zapp £26.40 2750 Torque
7 2510 1800 SY85STH65-5904B 34 Zapp £51.79 1500 Torque
8 2510 1800 SY85STH80-5504B 34 Zapp £75.60 2100 Torque
9 2510 1800 SY85STH156-6204B 34 Zapp £108.17 2100 Torque

Assuptions
Voltage set to 70V for all steppers
Phase current set to rated current of stepper
2510 screws have a minor diameter of 19mm
1610 screws have a minor diameter of 12mm
Speed is set for cutting
Fixing is Supported-Supported (I'll be using Chai fixings)
Gantry weight of 35Kg

Looking at the table I think my best bet if I want to go for 1800mm on X is row 5 which gives me 4000mm/min when cutting (and 7000mm/min in rapids). Row 1 looks like a good cheaper option though with only slightly reduced speed but rapids would be the same as cutting.

So, to all those who know a lot more about this than I do, what would you do? Please feel free to tell me I'm massively over-spec'ing / that I should build a smaller machine / suggest other parts etc.

Cheers