@csorrows Yup, that's where my research is pointing!
I took a closer look at the large prints I want to do, and it turns out only two of them won't fit on an FT5 R2.
The real issue is I need to improve my staging skills: I'm good at using the bed, but not the vertical. Simply tipping some parts up and adding supports lets a stock FT5 handle them (400 mm vertical is sweet). I also need to think in full 3D when doing my puzzle-piecing, instead of just chopping things off near the edge of the bed.
So now a stock FT5 R2 seems best: I'll take the savings from not going to 500mm^3 to pay for the very few truly huge prints I can't (or am too lazy to) do on the FT5.
Which means I'll probably also avoid using a 1 mm nozzle: 0.6 will be fine for most of the big stuff I want to do. I mean, once a print gets past 8-10 hours, I really don't care if it takes 40 hours (two nights with the day between, so I miss only one day of printer use).
I now figure I'll get quotes for any prints that would need more than 40 hours on the FT5 (puzzle-pieced).
This research did let me appreciate why the big Creality semi-kit printer costs $1100. I thought I could go better and cheaper with a jumbo FT5 kit, but I'd still be in nearly the same price bracket by the time I was done.
For that price, I'd be better off with a pair of FT5 R2 printers!
Thanks for all the feedback. It really clarified my thinking.