For example,in my 3rd edition Hornady reloading manual,using the #3031 150 grain Spire Point,in both the 30-06 and 308,the maximum velocity listed is 3100fps in the 30-06,and 2800fps in the 308,and this has been my experience of approximately 150 to 300fps difference between the two on my chronograph.
Your 30-06 barrel might have smaller bore and groove diameters. Who knows what peak pressure each had. A bad comparison. And Hornady's data is also skewed for the same reasons.
Nobody shooting their own factory sporters can get a realistic comparison between these two (nor any other two) rounds unless their ammo is loaded to and barrels's chambers and bores are at SAAMI specs, peak pressure's at SAAMI specs and the barrels are mounted in a fixed receiver. If using SAAMI spec ammo and barrels, then you're comparing just the two cartridges. When two different chamber, bore and groove dimensions are used as well as not verifying they produce SAAMI pressure specs, you're comparing too many dissimilar things at the same time and the data will be skewed. To say nothing of the muzzle velocity errors caused by humans holding the rifles.
SAAMI data for 150's from a .308 Win. at 62,000 PSI says 2800 fps and the .30-06 with a 150 at 60,000 PSI says 2900 fps. Both used the same batch of 150-gr. bullets. SAAMI spec pressure and velocity barrels for both are 24 inches long and have .3000" bore and .3080" groove diameters. Barrels are mounted in a Universal receiver hard mounted on a bench; it don't recoil at all. So based on each cartridge's design specs and compared in identical systems, the .30-06 shoots 150's a hundred fps faster than the .308 Win.