No matter what you buy I would lean toward the High thrust , Pro Kicker , Big Foot models . The engines run at a higher RPM when you are trolling so you will have better oil pressure and the alternator will be putting out a bit more juice. If you can I would also get electric start ,remote controls and tilt . I fish Lake O solo a lot and it is nice not to hang off the back of the boat in bad weather to work the motor . You can do everything right from the helm .
My boat is the best part of 3K lbs and the Yamaha 8T has all the power I need .
Good Luck !
JT