Wobblycogs CNC Mk1

[Jonathan]

I think I'm just starting to see how the multitude of factors play off against each other.

Which is precisely why I linked you to the spreadsheet instead of just telling you the answer , but it seems that's what you're after so...

So, to all those who know a lot more about this than I do, what would you do?

I'd use RM1610 and rotate the ballnut instead of the screw. From using the spreadsheet it should be now be obvious why it is such a big advantage to not rotate the screw.
The X-axis on my machine is 1700mm travel, with RM2510-2094mm ballscrews and rotating nuts. The highest it seems reliable at with 3Nm motors is 12m/min (so about the same as Jazz's but with substantially smaller motors), although it will intermittently run at 15m/min still with no signs of vibration/whipping problems. Tenson here has RM1610-1500mm and rotating nuts, so you may wish to ask him how it is performing as that should be a good indicator of the feedrate that configuration would get with 1800mm.

If sticking to a conventional setup it's not so clear cut. RM2510 and Nema34 is probably the safer option, but your table suggests there's a significant chance that the RM1610 and 3Nm motors would outperform it quite significantly you could go for the latter as it is the cheapest option and if whipping is a problem change to a rotating nut at a later date and keep the same motors/drivers.