Load, current, and wind all come into play, hard to give an answer. I had a motor die 1.2 miles from a ramp about a year ago and I have a 1448 Jon that is loaded fairly heavy. River runs 5-7 MPH and I was having to run upstream. I did have a good tail wind about half way and I made it in about 15 mins.
When I first got my boat, I had a Minn Kota C2-30lb mounted on the bow of a mostly empty 1448 Semi-V with a 9.8 Merc on the back. It would do ~2mph on speed 3, probably most of 4mph wide open.
Now, the same boat with casting decks, a proper bow mount TM, and a 25 Johnson with the same 30lb TM on the transom will do barely 2.5mph.