Thanks guys. Apologies, but I found it very hard to determine that the hx4700 actually had a usable serial port, I do feel like such a plonker now. But, even the User Guide that I downloaded said nothing about it, so I made that posting in desperation

Only yesterday did I found out all I needed and realised the hx4700 must surely be the best device for the purpose... so I ordered one in the afternoon (apologies for not updating this forum entry as it had escaped my mind).
I had also been to a fair amount of effort to determine which might be the best navigation software to run on it and I have to say that, even without having used it, all indications are that it must be mCU

(reasons: product maturity, makes allowance for paragliders and strength of forum). Thanks again, and looking forward to getting all the kit together