Before anyones response is buy a mud motor or surface drive, I already know. I run a 16' boat 25 hp motor. Its a little heavy with all the gear,decoys and blind. Clients almost always say something about the speed of the boat. What is a good prop for my set up? How do i get weeds under control? I do have a manual motor lift wich is awesome for shallow water.

make every boat a jet boat.  make all rivers longer.

I had the same problem with my 16ft with a 25hp fourstroke. I went from an 11x9.9 prop to a 10x9.9 prop. I picked up about 4-6mph on top end and loaded was about the same gain. My boat had to much prop and wouldn't let the motor run the rpm's it should. You need to hook up a tach to your motor load the boat down and see what prm's you are running. Then find out what it sould be running at and go from there. The larger the pitch the fast it will go on top end if you are running at the right rpm. The pitch measures how far the boat would go with one revolution of the prop. 11 pitch 11 inches, 8 pitch 8 inches. It's like gears in a truck rear end, if you put 3:20's in it, it would go fast on top end but slow off the start. If you put 4:56's it would be fast off the start, but slow on the top end. You need to find a happy medium, you won't both. If your rpm's are good loaded with a new prop, then when you are unloaded the motor will over rev. I went down one size on the pitch and it worked out fine for me, but every boat is different. Hope this helps.