thinking about a new Garmin head unit. Bring me up to speed

[trener1]

I have had both the 840 and 1040, I would say that yes the 840 would be the sweet spot of price/performance ratio.
Also just as a fyi, if you get caught riding in the rain and the rain starts messing with your screen (this has happened to me) you can lock the screen with a quick tap of the power button.