Re: >308 and .270 Win Bullet weights
Cant speak for the 270, but the 150 in a 12x barrel will do fine. I would recomend the ACCUBOND if you can keep the velocity up and the ballistic tip if you cannot. This is a great deer/antelope bullet at 308 velocities. The 12x is more than enough twist to handle the 150's. Palma gurus like 13x for the 155's and can be shot with even slower twists than that such as 14x. 12 is fine.
Long range shooting is a process that ends with a result. Once you start to focus on the result (where the shot goes, how big the group is, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.