The routes are re-calculated based on the map and profile (so route pref and avoidances)
So even if you transferred a route from your 6 to mine, if my default profile (motorcycle) has different preferences.
However if have enough waypoints, then it won't change. As there will be no way to route around it. Does that make sense?
If you've got two waypoints - home - local bike cafe, then it will change quite a bit. Depending on quickest/shortest/twisties etc.
Didn't realise you can pair a 5 and a 6 together to transfer a route. But I'd suggest it's not much more different than a map update sometimes changes a route very slightly.
Those routes I have with 64 waypoints change almost nothing at all from gps to gps even garmin - tomtom.
Ian.