For KDR, certainly Phoenix in '86 was a huge leap being the first one we built. It was incredibly heavy by modern standards and you could probably get the shell to pass safety without the frame. Pumpkin King was a great workhorse, but it sprung from Palooka, the first (that I know of) relatively light shell on frame for us.
If the secret to Zoo's speed is all wheels, which I'll buy since all those buggies are huge, why not make a smaller one? Seems like you could drop a couple seconds with better aero if what you're saying about wheels is true.