It would be interesting to see how the 6mm Lee Navy cartridge, used by the U.S. Marine Corps in the 1890s, would compare with today's lighter bullets and powder selection. It fired a 112-gr bullet at 2,650+ fps from a carbine.
Lots of tinkering with new cartridges for very little improvement over the original 6mm Navy, 6.5x55 Swede, 7mm Mauser, 8x57IS, .30-06, 7x64 and .375 H&H. But it has been a lot of fun, like race cars benefiting passenger cars.