-
Wonder if a factory reset could help? I would've suggested a new SD card or formatting the card but internal storage only, I've no idea if that's possible. I have restored my 800's storage before after someone provided the stock filesystem for it online.
Maybe you could try using a smaller subset of OSM maps and see if it makes any difference - that would at least eliminate the factory maps as an issue.
You've just made me want to load a route on the 1040 and see how fast it is...
Built in storage, route transferred from Connect app, Factory maps, all possible calculation settings turned off.