I prefer a single edged dagger over a fighting knife, because if there is not plenty of armor, then going quickly to something vital is fast enough. So a Rada brand of Tomato Slicer has five inches of length for the two or three inches of depth thrust, with the secondary role of cutting. Then the Aluminum Handle of between 3&4 inches will be good enough.
Then the sheathing for a blade like this will be the difficulty, because it will need to be custom created. While plenty of blades such as the Mora Knives at 4-inches will also work, for deep enough thrusts, combined with still cutting tendons, muscles, and blood vessels. With this being an example of avoiding, costly retro-engineering by using an established solution. Also known as the Mora-Knife, made to function well enough. So the Mora Knife would be the choice for the single edged dagger, with high chance of lethal damage even if through the other person's incompetency.
While the fighting knife will need to cut and keep cutting, so fatigue must be eliminated as a factor. To as a primary role cut through muscles, tendons, and blood vessels. And this lethal thrust if possible is only an extra feature with a fighting knife. So the CRKT ChanceInHell Machete is that fighting knife of choice, being different than a general purpose blade or even a sword.