I was going to dazzle you with my explanations of displacement hull speeds...theoretical hull speed versus cruising speed...but...you've already got excellent responses. For the average person efficient cruising speed is by far the most important. If all you're wanting is a craft that is hard to paddle just so you can get a workout then consider a raft. I speak from experience. In a New Mexico raft race, my construction crew, who out-muscled any other three teams, was soundly trounced by a wimpy McDonalds team because their raft was a far better design. Brains are better than brawn any day.