The Squashtail is a surfing super star that happens to be able to run rivers well enough to get to the playspot. It's actually a bit suprising how well it paddles downstream. Take a moment here and really examine the rocker. The upturned nose makes it super friendly on waves and holes, and the low rocker tail gives it unparalleled speed. The overall PROGRESSIVE rocker lets the water "see" the hull as one long, continuous surface, so it acts like a longer/faster boat.
The Air 55 was a good attempt at gaining some speed out of a short boat (for its day), but it loses some speed because it leans more towards that "3 stage" rocker. It's a compromise between some speed and that grab/release process that creates some bounce (but slows things way down).
The Stinger takes big strides towards solving the speed/bounce paradox. There is an arguement that you have to have either speed OR bounce. This is somewhat true, but they can be closer than everyone will sell to you. The progressive rocker on the Stinger lets the water see the hull as one continous surface, thus letting it act like a longer/faster boat. The quick, but SMOOTH upturn of the tail lets you rock back, riding up on the tail, pointing the nose to the sky and gaining the bounce and air that you desire.
An added bonus is the huge bow rocker. It makes for an easy paddling river runner. Letting you leap over waves and small holes.
The Stinger is a highly rockered boat that is as fast (if not faster) than the Air. So you are getting the best of both worlds, and thus a much more fun boat.
Take a really close look at these boats. It's easy to tell which one is a pure surf boat. But also notice how boxy the Air is. Imagine the boxier corners when you try to edge your boat. The kind of trip things up a bit. There is a reason why surfboards have a continous curve in their template (the view you see here). As you lean a board on edge (or a boat) the continous curve creates a graceful bent line that can be changed by leaning forward or back. A staighter edge had a deflecting tendency that adds alot of drag to a turn,making for a choppy ride, a bit of unpredictable bounce, and killing lots of speed.
Why add uneccessary length to a boat just to gain speed, when there are much more effective ways to get faster. Template and rocker are basics of design and still two of the most important aspects for gaining as much performance as possible from your new kayak,... especially if you are going to go out and spend money,and want a GENUINELY new design.