I just bought the Helix 5 for ice fishing and for my boat. The screen is fine, especially in the ice shanty. I have not been able to see it well in the daylight. I think it will be fine for my boat too as I plan to mount it right in front of me in my tiller boat. It will be less than 3 feet away, close than in my shanty. I need to fiddle around with the screen colors so I can see it in daylight. I looked at the 7, but thought it was just to big to haul around all the time.
I swapped out the battery to a Lithium Ion and the longevity was amazing!