[Sorry for whatever got my previous post deleted, not sure why]
Thanks Sam, your post is very encouraging in that it is possible to get high accuracy at scale.
Now that I've figured out the squaring, tuning, leveling, tensioning, circles, x & y steps, feed rates, flexing, tightening, torque needs, etc. I've also mounted my Makita router back as my spindle.
I just cut a circle I'm happy with regular acrylic at 6mm depth. That's almost 1/4" thick very much sufficient for what I need. HDPE is easy at 3/4". Wood is just slightly slower than HDPE. I haven't cut aluminum or CF yet, that'll be another set of challenges I'm sure but then again I won't be cutting aluminum. Engraving is very simple.
There is an acrylic called Makrolon by Bayer which is really tough at 1/4", I have not been able to reliably cut that using my Proxxon Pro spindle. Maybe now with my Makita router I can.
I'm grinning like a kid in a toy store

I'm ready to build my v2 SO2 at 1000 x 1000 mm span now.
I actually have the 1800 mm Makerslide so I can account for the extra wheels, plate widths, etc. Then use NEMA 23 motors, and the 9mm belt upgrade.
Would appreciate info on 15mm belt too (and pulleys, and idlers).
My end goal is to cut CF for production parts of my quadcopter aircraft designs. An aside is SO2 makes a great platform for a large scale 3D printer with space for multiple extruders (parallel printing of parts). Finally, at 1800 mm span, I can finally build a 100W laser cutter.
To save space, I'm thinking of placing all 3 subsystems on the same Y rails with separate controllers each and an A/B/C switch.
Whew, I've got at least 3 months of work to do. One thing at a time, I can work with my v1 SO2 now.