I had created a route for a club ride. About 375 Km. The time estimate using the HERE Gold map is 5h 49m. When I sent the map/gpx to another user, he reported the time estimate was 6h 19m. I tried switching to the general map and got the same estimate of 6:19. I then switched to the TomTom map and got an estimate of 5:18. That's an hour less than the general map. The distance remained fairly consistent and stayed within 1km for each map.

Why is there such a big difference in time estimates?