Just to clarify if you don't mind.....you manage ok with the autoroute facility and 50 waypoints? How do you plan your route, on bikehike or similar sort of thing?
Painstakingly in Mapsource, and then sanity-check on the unit itself, as the algorithms aren't quite the same (don't even think about using Bikehike or anything that isn't using exactly the same map as your Garmin). It's a bit of a black art, as in some places you'll need to drop a lot more routepoints than others to keep it to the intended route. However, this means I get the auto-routing display with turn arrows, which I find much easier to read on the bike (especially the USS recumbents, where the Garmin is mounted relatively far from my eyes).
The reason I ask is, all the online help stuff says not to use the autoroute option as 50 waypoints is not enough for audaxing.
I rarely ride more than 200km at a go, so that's probably a reasonable statement. However, there's no reason you can't represent a longer ride as multiple Routes - if you split them at logical places (ie. controls) it doesn't add much faff.
The main issue with the autorouting, apart from not spotting that it's chosen some bizarre unintended route at the planning stage, is that it can't handle deviations from the mapping. So un-mapped cycle paths, contraflow cycle lanes and the typical cross-the-dual-carriageway-as-a-pedestrian manoeuvre mean selectively ignoring the Garmin's instructions. I create an explanatory waypoint in those situations.
If it's an Audax or something route-critical, I'll generally create a track of the route first, and upload that to the Garmin too. That way there's a line on the map to sanity check the autorouting instructions against.
While it's quite time-consuming, doing this amount of homework does mean you have a good idea of where you're going on the day, rather than blindly following a GPS/routesheet/fellow cyclist.