I'd be interested in hearing from people who have owned both of these GPSs..

I currently have (and love) a NAV-III, but there is some room for improvement, and I'm considering moving up to a NAV-IV.

Things I think could be improved:

- A built in MP3 player. Since I got the Schuberth SRC Bluetooth collar, I've tried using the built in FM radio in the SRC. It works - sorta. Range isn't great, and FM likes to be line of sight, so using it in mountainous areas is about impossible. I can see where tunes make the slab go faster - so an MP3 player would do it for me. Problem is - the NAV-III can't stream the player on my Android phone, and the SRC has to use the GPS as the "hub" if I want to have phone and GPS spoken announcements.

- Sun behind me visibility. The NAV-III can completely wash out if the sun is directly hitting the screen. I rode someone else's bike with an early Zumo, and from memory - the screen was much better in direct sunlight. True?

Things I question on the III vs IV:

- On a recent trip to Canada, I was riding with a friend with the NAV-IV. We also had the intercom function of our SRC's setup so we could talk bike to bike. He had problems with his NAV-IV dithering on several large intersections in Canada (and to a lesser extent in the US).. the NAV-IV has lane display, and at times it had him jumping from lane to lane, or it would tell him things like "Take Motoroute-15 North, take Motoroute 15 South, take Motoroute-15 North, etc. etc.. It simply couldn't make up it's mind. My old NAV-III (with the latest maps on it) didn't have that problem, so it ended up with my taking the lead.

- I have a good friend who is somewhat renowned in the IronButt world, and he will only use a NAV-II or NAV-III. Why? Dunno exactly but he said it was the best one out there. Strangely there is an Ebay auction going on for a NAV-II right now, that last I looked had 36 bids and was $460, with a few days to go. That seems just crazy to me, but does someone know something I don't?

FWIW - I'm not too enthused about the Zumo 550, 660, etc. I seem to have seen too many reports of firmware problems with them that have only slowly been resolved (if at all) by Garmin. They're probably fine units, but at the moment, I'm only considering the NAV-IV..

So - who has (or does) owned both? And your impressions?