Thanks Jazz that's spot on what I needed and really helpful, I think I'm just starting to see how the multitude of factors play off against each other.

I suspect the speeds in that table are a bit low because I went for supported-supported and was quite conservative with the limit.

I'll have to get the calculator out and see what the financial damage is if I stick at 1800 on X :-). Whether I build it 1500 or 1800 I've got to get a load of stuff out of the workshop so I'm tempted to stay with 1800. I've also got a project in mind that would need more than I think I could reasonably do on 1500 (lol, two bad excuses)

I realized today that my frame design makes mounting the screw bearings really awkward so it might be back to the drawing board for that. My aim of getting the mechanical side of things done by the end of the year is looking wildly optimistic already