Will await your views with interest jinxit! I didn't want to fit a 140/80 due to the higher gearing effect and reduced clearance between tyre and swinging arm.
Incidentally, a prominant supplier assured me that the 140/80 made no difference to tyre diameter because the "80" was an absolute measurement (80mm) and not a percentage of tyre width!!

My new supplier is Mick at tyre-finder.co.uk.