"I agree with Michael that sometimes cats feel like they're planing. My cat has deep V hull--at least as deep as your g-cat, but symmetric."- ejpoulsen

G-Cats also have symmetric hulls- and not a single "round" hull section to them. They are super-deep-V bow-to-stern and use the bottom of that shape like a keel to go to weather. That keel, and a monstrous jib (since it attaches low at the bow beam instead of high at the bridle) really give the boat a surprising windward ability.

With "phatkid" crewing for me in some fairly high winds and flat seas, I've had the boat near 20 knots and it at no time felt like it even wanted to plane.
"Phatkid" has an aversion to trapezes though, so I never did get to crank in the main sheet and bear off to a broad reach

Thanks for all of the information- I think I'll check out a few books and soon be able to post a nice, informed reply to the man who claims:
"Whether a boat is a planing hull or a displacement hull is not a matter of opinion, but definition.... I only have a masters degree in engineering so I am not qualified to engage in the establishment of new science."