Steve, I am with you ALL the way with the larger screen, so much so, that that particular preference was also part of the reasons I was so ANTI Garmin for well over a year. Now that the software upgrades have made significant improvements in the behavior of Garmin, I am able to "live" with it, JUST. That said, guess what is in the back seat of Big Butt, with S & T loaded with my route loaded and in suspend mode. Yep, the computer. I have pulled it out a couple of times and used it while talking Al through or to a destination. Personally I have no trouble with having the computer going while he is driving or viceversa, Patodonn, but, fully respect your comfort level on this, and if it makes you uncomfortable, then you have to do what you have to do. We have been in a couple of situations where I needed either a big map, or S & T, and S & T won, cause I can make the detail go up and down so quickly, one way, then the tuther!
I have been known to have out campground book, Exit Authority, big Travel maps, and the computer and the Garmin, all at the same time.