Let me interject something here, too. The AR-15 (before it became the M-16) was first chambered in .222 Remington. The army thought the effective range should be greater, so the .223 Remington was developed. Some references mention a .224 Remington, which might be the same thing. You realize that other armies actually used it in combat before we did and still use it. That's not all they use, however, having seen no reason to quit using full-grown machine guns. Anyhow, the .223 started its killing career as a military cartridge, same as the .308, and at nearly the same time. Oddly enough, the same rifle (the AR-15, that is) initially replaced .30 carbines in the first two armies that used it.
Personally, I think the .223 could stand to be improved with a larger caliber and heavier bullet but you would immediately loose something, no doubt and what is always hard to second guess. You can't get something for nothing. Oh, and the idea about one shot, one kill (sniping excepted) is sort of a 1914 concept and that mentality would not accept Thompson sub-machine guns.
For everything else you might care to carry around, the 7.62 is fine. I pretty much see no need for pistols.