I have a Superjet. I love the boat. They came standard as quarter stringer boats with a full floor(foam filled) they are all built like a brick shit house. As far as pre purchase your inspection should be the same as any other boat.( stingers floors etc) a lot of SJ's I hear of have a porpoising problem due to the hook in the hull and my guess is being magnified over time from sitting. My boat with the orig 460 topped out at a gps'd 72 mph when the the motor let go. So they run pretty well. For a heavy boat. Even though they are a very shallow v bottom with an extremely shallow entry they(mine) still handles your average afternoon chop pretty well.
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