Thanks for the feedback, Ralph! I'll research the Nobel SLA, but I'd be kind of shocked if I can afford an SLA.
Thanks also for the comments on the Ultimaker Original. As I understand it, the Plus version comes with the heated bed you mentioned. I have been wondering whether my desire for 20 micron resolution is overkill - sounds like you think so.
The other machine that has caught my eye is the FlashForge Creator Pro. Supposed to be really reliable. 100 micron min Z resolution, but a really stunning (to me) XY precision of 11 microns. And I'm intrigued by the dissolvable supports for overhangs that it can do.
What do you guys think about the FlashForge? I see it's got a subforum here....
Thanks again, Ralph.