Imco has a 6 inch fin vs 8.5 sporty. Thats about 1.5 mph of it. Then the water pickup is smaller. Thats another 1 mph maybe. ( but you may over heat your motor in some cases) The rest is the point and shape. But its is all at about 100 where yiou see the differences ( from what I have heard) . So whatever you can get a deal on. Remember with an imoco you could have a sketchy handeling ride at somes with the shorter fin