okay the smooshing does seem to be helping.
Also dropped temp back to 240, speed down to 45, extrusion multiplier 0.9 and first layer height at 100%.

It'll take a frigging age to print the larger moulds, I guess that's why I have extra printers :-)

I'll stop cooling next, can't see how that's going o help - but it's something I haven't tried yet.

is there a particular pet-g colour you think works better than the others ?

With pla, for me red is always much better and gives way cleaner and better prints than any other colour.