Pop into Bi Mart and get the 30# for $100. I believe that they have the #40 for $149
I got the Minn Kota #30, you get the power meter FREE when you register the motor.
So far its done nice with my 9ft Rogue toon. Shouldn't me much difference on a 10.5 toon.
You also need to think about the battery that you are going to be using.
Large marine / rv deep cycles are HEAVY and cumbersome. Medium RV batteries are still weighty, but work well. All Deep Cycle seem to be expensive. The best out there looks like the Optima Gell Deep Cycle.
I have been testing my #30 with a lawn tractor battery. I have so far got 3 hours trolling at setting 1 and the battery was still half charged. I am going to run with a lawn tractor battery on each side (to balance the toon) so i KNOW that i have a reserve. Also note.. most of the lawn tractor batteries are made for STARTING not DEEP CYCLE so DON'T drain them past 1/3 charge.
I have also tried an "emergency pack" which is made from 3 x square torch batteries (12v) in parallel . I got 25 mins of power on setting 1, 15 on medium and 4mins on highest speed, note: one battery on its own doesn't have the ampage to turn the electric motor. BUT>>> its a nice small emergency pack.
On that note.. multiple batteries should ALWAYS be wired in parallel, both neg terms attached to one wire, both positive to the other. Do it the other way and you will fry motor.
hmm... i went rambling on.. but, hope this helps
I have no idea about using them in 'brackish' water, but, these are made for bass boats, etc, and they go though all sorts of cr@p.