I think you've basically covered the bases with this deck, J.
10ofclubs mentioned metric measure - you could make it a background pattern on the faces, in a light color like a pale blue on white. This way you have English and metric measures. Concentric rings extending out from the corners would make sense, since it's most likely that the card will penetrate on a corner impact. Make the Jokers or at least the ad cards with actual, accurate rulers printed on them - never hurts to have a measuring tool.
See if the manufacturer can make your cards in a way that allows them to be laminated AFTER they've been cut from the sheet. This would allow you to apply laminate right on the edge of the card itself, strengthening it to help keep its keen edge and aerodynamics. I recall hearing that some old-school decks were done like this. Even if it's a secondary lamination done after the standard manufacturing process, it would still make that edge stronger - and could give the card a little extra heft for penetration power.
Do some simple aerodynamic tests of various embossing patterns that would be available to you when having them made. To my knowledge, a simple dot pattern similar in appearance to the surface of a golf ball would be best, but what do I know - I'm not an aerodynamics engineer. It could be possible that one pattern will give you a slight edge over the others. Another possible idea to test - would "faro-style" sharp corners be more or less effective for piercing than modern rounded corners?
Cartamundi may do a good job and have the right stock - but Fournier is capable of some very precise, high-grade card manufacturing, as anyone who appreciates a pack of Fournier 605s can tell you. The stock they use on the 605s is not just stiff and strong, it's actually water-resistant - many people use brief submersion in water to clean the cards individually . I'm thinking that if any company can make you a playing card that's the closest thing to armored you can get while still being made of paper, Fournier is that company.