I find with backlight turned off, having the map screen on consumes very little more power than with the screen shut off. (Thus, my comments on backlight in a previous post.) I do not remember if I did that test with my 62S or 64, the 64 is the one I use now on my bike. That said, I think that was the data screen, not map screen. I might have to re-run this test with map screen.
But, as I noted before I am not using a cycling specific model so I have no clue if that changes the power usage.
This is on a bike tour, not rando event. Bike computer next to GPS, left of that is a HRM.