There are a lot more .30 caliber target bullets inteded for long range shooting. Most 270 bullets are designed for hunting There is more information available to guide you setting up a 30-06 for long range shooting. Heavier .30 bullets are less effected by wind at long range With good bullets, the 270 will always shoot flatter, but that is not a factor in long range shooting. As long as you are shooting at known distances you can always adjust your sights.
There are a few 270 bullets designed now for long range shooting and I believe that it is theoretically possible that both can be equal. But the 30-06 has been used in this role far, far more often and the information on how to do it is there. Getting a 270 to do it would be harder since you would be doing a lot of your own research on load data etc.