Who said anything about a light barrel? My Rem 700 is the Varmint Synthetic, with the heavy barrel. With a used Tasco 4-14 scope I shoot under 1 MOA (when I do my part correctly) using Sierra 168 gr. Matchkings. I have yet to develop my own loads, but hopefully will this spring & summer. I expect that this will not only cut my cost per round, but result in a bit better accuracy. I am hoping for a consistant 3/4 MOA.
I agree that the rifle is more important than the scope, but the latter can help a lot at extended ranges, as you've indicated.
Aim small, miss small.