Hi all, thanks for the advice.
But just to clarify, in order to get the 6 knots I do need to push the throttle into the stiff (more than tickover) zone so the tickover is fine, I don't believe it to be running fast. (I just didn't notice any speed when in tickover, but this may have been due to the conditions). I think I'll just start taking it out and playing with it to get used to it as it is a bigger boat/engine than I've previously been used to.
And I'm usually ok with a trailer (think lack of practise and a bit of stress started to play a part), but that trick with your hands at the bottom of the wheel and moving them where you want the trailer to go is useful!