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It would be light, fast and have enough capacity to handle big waves with a load. I would go with a Kevlar boat in the 161/2-18 foot range, not too beamy like around 35-36 inches. Flat bow and stern with maybe around 13-14 inches deep. There are many boats that fit that description. A straight keel line is important for the flats. I like the Wenonah MN II and the Souris River Queticos
We used to trip for seven days in a 15 foot Grumman. Later the trips got longer to two weeks and we needed a little more room. 16 would be ideal. 18.5 feet is really overkill for a week long trip but I realize the MN II is the favorite BWCA boat.
Speed on the water does not matter unless you single portage and have unloading, loading, down to a system of no waste of time. I wouldn't pay as much attention to the speed of the boat as to your speed.
I have the deep brethren to the MN II, the Odyssey and its been handy on two week unmaintained portage trips and on Lake Superior and remote far north trips. But not so necessary in the BWCA. Except as you get old. We could haul the Grumman easy in 1973 and did. Not anymore! We can still haul the Odyssey nearing the age of 70.