With the TA maps I didn't find a GPS worth carrying. I sent it home after a week. The AC maps were easy enough to use that we felt no need to supplement them with anything but a state map picked up each time we entered a new state. We did intentionally go off route once in a while using an alternate route that the AC maps did not cover and that was the only time the GPS would have been used.
On the 705, I don't think it is really a good design for touring. Keeping it charged will be a hassle and the features aren't really there for touring.