Rotaryphile,
A subsidiary question please.

I measured the trust myself using kitchen scales(Put plane nose down on scale, measure weight, turn on engine, measure new "weight", and much to my surprise, it didn't seem to matter what prop. I put on. Your answer has given me the clue - I was measuring the thrust whilst the plane was static. So, given that the trust was the same with all props, should I go for the one with the biggest pitch to give me highest thrust when at flying speed?

Cheers

Chris