Any question answered...

Tufo sewn-up clinchers don't stress the rim in the same way as real clinchers, so feel free to run them at stupidly high pressures if you prefer discomfort and poor handling.

With proper tyres, I'd probably not exceed 8 bar with 20mm tyres and correspondingly lower with bigger tyres on vintage rims, they used to build the sidewalls a bit lighter in those days.

Cheers Tester.