Hey, Chiselman and All:
Thanks for an interesting discussion.
Mikey177 beat me to the punch in referencing the P'Kal, which I believe has the exact blade shape Chiselman was describing. My testing experience relies primarily on using various shapes of training blades with partners and doing live-blade cutting on Pork Man and other targets. Training with partners validates the suitability of a particular blade shape for my preferred system of tactics. When I've tried radically curved hawkbills with MBC skills, they tend to snag on limbs, preventing a clean follow through and requiring you to "back off" on the cut to finish the motion.
When the same blade shape was used in live-blade cutting on Pork Man, the problem was even worse. If I started the cut with the heel of the edge, as the edge cut into the tissue, the blade point would hook over the dowel that simulated bone. At that point, I either had to articulate my wrist to an uncomfortable degree to contour around the dowel, or I had to back out of the cut.
Hawkbills with significant curve to the edge do have the ability to puncture with the point during a cutting action, much like an animal's claw. They then shear from the tip to the heel of the edge. This can be a very powerful cutting action, as long as you precisely control the depth of the initial penetration so you don't hit bone. That takes a lot of skill when targeting limbs. Radically curved hawkbills also completely lose the ability to thrust with conventional body mechanics and require specialized technique.
Hawkbills with a slight concave to the edge profile are much less prone to snagging and can offer slightly increased pressure at the very tip of the blade. The trade-off is a lower point profile that, again, makes thrusting with conventional technique more difficult. For edge-out applications, I wasn't able to tell much difference between their cutting performance and the performance of a good Wharncliffe. From an angular thrusting perspective, I found I often hit with the spine of the blade instead of the point. Again, it depended upon the exact profile of the knife.
Circling back to the P'Kal, it's important to understand the dynamics of the blade curve and their effect during various tactics. The curve of the P'Kal blade actually replicates the radius of the arc of the arm from elbow to hand--the motion of the backhand "P'Kal Jab." This puts the point below the bottom of the fist for maximum energy transfer and accuracy with that tactic. Interestingly, this is the same principle of the Warrior knife, but that arc was based on the full motion of the arm with the origin at the shoulder and incorporating a secondary bend at the elbow. Actual P'Kal tactics involve thrusting and then shearing or clearing on retraction. If you want to hook limbs, you articulate your wrist. If you want to cut, you simply pull back. While devastatingly effective, they're harder to express as true defensive actions in a self-defense context.
Where Chiselman's idea really shines is with non-locking folders. When I travel in Europe, where the carry of one-hand-opening, lock-blade folders is often illegal, I carry a hawkbill slipjoint as my folder. The slight concave curve of the edge amps up the blade's cutting power, keeps the blade open during use, and "reminds" me not to thrust with it. Even though it doesn't lock, all the core techniques of my MBC system can be done very effectively with it. During the weeks before I travel, I also train exclusively with a folding trainer that has a broken lock. It will "stay" open, but not "lock" open. I reprogram my tactics to eliminate thrusts altogether.
One final point--literally--is that many people are critical of the Yojimbo 2 because of its perceived tip weakness. Most of the people who complain about it don't actually own one and haven't broken a tip, but that's apparently irrelevant. Nevertheless, if you wanted to incorporate a slight hawkbill concave to the edge, you'd run the risk of making the tip more fragile--unless you added "meat" to the spine of the blade above it.
Like most things in life, it's a compromise... Again, thanks for a great discussion.