I just finished reading The Rifle Book, and i read all his books except the Shotgun Book. He writes 6 times more words with 3 times more appreciation for the .270 than anything else, and he writes at least 30 times, that the best caliber does not exist, only best suited rifle, with which the hunter is familiar with and can shoot well. He wrote more about the quality of bullets and importance of marksmanship and he emphasized that a poor bullet or a poor shot is useless, even from a "good" caliber. In fact, in the Rifle Book, i think that he wrote that 30-06 is great because it is versatile in terms of bullet weights, but he went on to say that for every bullet weight or hunting task there are other calibers that do the job better than 30-06. I agree, the 30-06 is like the German Shepherd, good at many things, but not the best at anything. And that was 1962, mind you. Jack would have been thrilled by the 7mm-08, or the 6.5 Grendel and the new ballistics from so many new powders, and the copper bullets. In Jack's time, Barnes was making explosive lead bullets.
He was also quite critical of the 30-06 for shooting different bullet weights at different POI, which was not the case with his .270 at that time.
And yes, i am sure that he appreciated the 30-06 too. It still does not mean that it is best or superior. Further, it does not validate your choice, Swampman. Just because O'Connor wrote that 30-06 is great it does not make you smart for choosing it.
I respect a lot hunters who choose rifles because they fit them, are apt to the task, are well built, and learn to shoot them well. I respect hunters who choose a good (for them) 6.5 over a shoddy 30-06. Caliber comparisons are useless. There is more to hunting, marksmanship, etc. than caliber.
I have reloaded for a 30-06 owned by a friend, and i got to shoot the rifle. He asked me to load bullets which do not ruin too much meat...I did not hunt with this rifle, and i do not own a 30-06. After shooting it, and one other Mauser 30-06, after handling a few 30-06 Rem 700s, i can tell that i would never ever want a 30-06 and i would never take it over my 6mm Remington. For the really big stuff, i would get a .338 anyway. Oh, wait, i already did.