The average temps for the beginning of October are a high of 55F and a low of 35F.
Portages will not be very long or very many, as far as carrying heavy loads. Hiking will likely be day trips or short hikes away from the shoreline. Loads will be a light day pack. At those temps, I probably won't need much insulation value in whatever I wear on my feet.
Not sure what an "Alaskan" boot is, but I was thinking something similar to a "Muck" brand boot. The downfall would obviously be lack of breathability and support, but the upside would be staying dry in the water and mud.
The advantage of 5-buckle overshoes would be that I could wear comfortable, supportive shoes/boots underneath, and still have 15 inches of waterproof-ness.