CB... out here on Guam there has been about 10 boats that have repowered with the Suzuki 140. One of them is a very good friend of mine, his boat is all 3/16" to 1/4" aluminum and is about 22' in length. The engine is mounted on a gill bracket/swimdeck. This boat has a shallow draft. The prop is a 15 pitch, 13 1/2" diameter. at this point after about 50 hours the average fuel consumption is around 3 + gallons an hour. From what I hear everyone is reporting the same.
Now my reservation is... I drive this boat alot and it once had a 200 hp Mariner... we use it primarily for taking divers out. This boat can take more weight than mine so we can take 6 divers (plus me the "Boat Man") 24 tanks, 7 coolers (one of them with ice and drinks), water, ice and fish.
Before with the 200 I could cruise in at the end of the night loaded at 4500 RPM with throttle to spare to 5600. With the 140 I am at 5400 RPM and about tacked out. I will say I like the 140 and because of my exposure to it I am saving for a 225 to replace the 200 Merc on mine. But because I go out long distances, have tendency to catch a lot of fish and have been in 8 foot chop coming home, I feel the need for the horsepower.
On a different boat that another friend of mine has, he repowered his 20' fiberglass boat (I don't know the make) with a Suzuki 140 (I have not been on this boat). He has propped it with a 17 pitch 14" diameter prop and is very satisfied with the performance. He also is claiming 3 + gallons an hour at about 30 hours so far. He does not take out any divers like we do, he only trolls.
Hope this helps with some of your curiosity about the Suzuki/Johnson four strokes. Guam is a very good testing ground for this sort of thing... if there is something venerable it will be discovered fast here because of our harsh saltwater environment.