A lot of factors come into play concerning speed. You have a theoretical hull speed, I believe it's 1.34 times the square root of of the waterline length....but....it can be exceeded (or not) depending on the hull and motor. The motor being the paddler. Someone else can probably give you a lot more, better information, but I believe that cruising speed is a lot more important than theoretical top speed. As a result of that I design for 1 times the square root...and try to concentrate on an efficient, easy gliding hull. I don't think an inch here or there is going to make much difference. Read everything you can from some of the good designers, mimic (not steal) the good points about their designs. Some of these guys are good...it's just too bad none have a plan like you need. You might also take a look at the canoes (and kayak) made by Verlin Kruger (I don't even know if he is still alive). To me they are sweet. Great expedition, or cruising hulls. You might get some ideas from these. Run a search on google for stuff by John Winters (I think thats his name). He has some good information.