The Japanese Model 97 Arisaka was 6.5 mm. The .30-06 trumped it every time. A .30-06 with standard AP could penetrate a palm tree and kill the man behind it. The 6.5mm used by both the Italians and the IJA was underpowered, and lacked the cross-sectional area to rip parts off, which is the function of a rifle. Hit a man with one round of .30-06, he is going down. Hit him with several, like from a M1919 Browning, or a BAR, and he will be separated into several steaming parts.
The M-1 carbine was too hot for a pistol round, and too wussy for a rifle. Little girls and the Army liked it though... Recoil being such a major factor for beanie wearing metrosexuals...
I bought a book written by a Colonel who was with Merrill's Marauders in WWII. They loved the .30 carbine because it was so handy in the jungle. The guy also did an analysis on the Japanese arms in the book and basically said that except for their mortars they were crap.