After much research, it appears that while tomtom is most popular, Garmin seems to be the most highly thought of satnav.
I have submitted some questions to garmin (who for the record, already support some S60 devices), and hope they will answer promptly.
Anyone used Garmin products commenting would be welcome, especially anyone having used it on a symbian device.
The only time I've used Garmin products is in private pilot aviation and tank combat years ago.
Needless to say, cell phones/mobiles weren't part of the equation, but since Garmin also uses MGRS (Military Grid Reference System), I've found them to be on par with the official military GPS systems which tend to be huge and clunky, even to this day.
They work damn well, but I don't know how their road navigation is since I've never used that part.
I had a Garmin and found the software wasn't a patch on TomTom. The maps had more inconsistencies, the refresh rate was appaling so you'd get past a junction and then if there as another soon after, have no idea of where to go, and their maps looked terrible. The user interface was infriendly and the ability to add POIs etc limited.
All in all a bad experience and I am glad to see the back of it.