I've got an Xpress 1546, and Brine put his long shaft 10hp on mine (I actually need a short shaft with my boat).. with both of us and gear it moved us 7mph according to a handheld gps.
This past weekend, I had my 71# front trolling motor, a 50# and 55# transom trolling motor (my usual setup, and it runs me at 4.8-5.0 mph by myself).
We added a 24v 82# transom trolling motor to all of that and it still pushed me and another guy 4.9-5 mph... so I'm thinking 5mph is the hull speed of my boat.
I'm going to add one more 50# transom TM, and 1 more battery just to see if it gives me any extra boost. I really want to get rid of all 3 transom mounts, and maybe move up to 1 101# or 80# motor just to cut back on batteries... more than likely leaning towards the 80# just because it runs on 2 batteries.