Okay from the best I can tell using a quad-folded paper towel (cheap brand!) on a hard chair, It looks like center to center is somewhere around 5 1/4 inches or 135 mm (hopefully that equates?)

So I went to a bike catalog thinking I'd start seeing measurements to compare to . . . but none had it!
Jeez,
Anyway, thanks for the hlep out there
If this measurement means anything as far as a "good size seat" let me know