Right, getting somewhere.
Had a good chat with Coastalrides - who supplied the engine orginally. My D3 should max out at 4000rpm - it doesnt so, I'm over propped as I can only get 3600... so thats good news.
He has also got a 2nd hand 4 blader that isnt much money - Ive bought it and going to give that a bash - if it works and I want to upgrade to a SS one he will take this one back in exchange, or if it doesnt work out, he'll take it back for a 20% restocking charge - sounds fair to me.
Fingers crossed with a 2" reduction in pitch and an extra blade I should get more revs, a better hole shot and a better cruise.
I'll know tomorrow as it will be here in the morning!