A lot depends on if you hand-load or not. In factory offerings there is not a lot of difference between the two cartridges. Hand loading for the 30-06 in a modern rifle does however give the edge to the larger capacity round, especially with heavier bullets. The 308 with 165 grain bullets pretty well maxes out at 2650 - 2700 fps. The 30-06 can safely propel those bullets at 2900+ fps, a gain of 75- 100 yards in extreme range, With 180 and heavier bullets the spread is even larger.