Thanks m_c, I see your point.

I've just been out in the cold trying to check the pitch on the ballscrews, it seems to be 2.5mm, so with the drop from the belt that's 1.5mm per stepper turn. At the advertised 2000mm/min that motor will be running at 1333rpm, so fairly humming, it's also a mad 0.0075mm per whole step. It looks like I'd need to change the pulleys to go faster, there seems to be space to go 1:1, so maybe that's also one for the future.

I'd been contemplating 'Leadshine' AM882 drivers, but I'm wondering now if they're a bit too much, I guess they'll give plenty of headroom :D