Main goal is navigation: following downloaded courses, especially for gravel races. So fast, correct, notifications of turns is essential. But also for mtb riding , so Trailforks maps are a must (but I think all Garmins have that?).
Prefer not to have it too big or too expensive and decent battery life, say 12 hours of continuous navigation but no need for multi day (will recharge if that’s needed) run time.
Additional navigation features like POi and rerouting on the bike computer also required.
I want to stick with Garmin as my wife and I each have a Garmin Watch and I have an Edge 530 already and a Varia radar. So, to keep ease of use with this second computer for us, I want to stick with Garmin.
Since your primary use is maps/ navigation (same for me), I’d go with the 850 (or maybe 840 if still available). Touchscreen for panning/zooming is indispensable, IMHO.
Same answer. I have a 1040 solar and the navigation is really good, both gravel and mtb. I use it when doing gravel sportive type events where a fox file of the route is supplied. Very clear and never got lost. Battery on the solar model is very very good.