Actually, the money you would spend to by a .30-06 action, .308 barrel, gunsmithing fees and what not would be very prohibitive.
Just a suggestion, have you considered selling the .308 and the associated reloading dies/casings and then just buying a nice .30-06, dies and brass?
You would get the "extra" performance that you desire and still would only be reloading for 1 caliber. Plus, the .30-06 is able to do anything the .308 can do at lower and higher performance levels.
Just my :money:
Good luck and I hope this helps,