On a lake, a 30 ft/lb thrust will push you if there's not much wind. A friend and I had a 14' jon boat and used a 28 ft/lb thrust trolling motor on it for years at a lake. It goes. It doesn't go fast, but no trolling motor will. Fast is not their job.
That said, I generally use a 45 or 55 ft/lb thrust trolling motor on my canoe now, when I'm not using a gas engine. The gas engine is better, but is not welcome at all places.
If you are in current, get as much push as you can.
The advice with the Maximizer is good in the previous post. You will get more effective run time with a Maximizer. Using it with a good battery is important. A used car battery will work, but it won't work well and it won't work long. The advice on preventing hang-ups and flips in the previous post is also good.
Touring Kayak Paddles
Heel and Pegpads™