I prefer to neck down if possible, always tightens up the neck to chamber fit to some degree because the neck will thicken. Make sure you have enough bullet release though.
While up in Canada hunting with Richard Graves, he had a 7mm-08 AI come in that he had built. He wanted to use 308 Lapua cases but was having the case shoulders collapse when he tried to size them down.
One little trick, if your using a standard set of dies, he had Redding, use your seater die as a step down die to form brass. it is machined several thou over what a sizing die is and offered enough increase in neck diameter to neck the cases down easily without crushing the shoulders.
Then follow up with the Full Length die and your ready to roll. Remember though they have to be standard dies as they have the same heat treat in the seater as they do in the FL die and will not be harmed by doing this stepdown proceedure.
This problem is because of the annealing on the Lapua case neck which makes them very soft. Great for long case life, not for sizing down or up.
Just a little trick that may help you as well that we figured out playing with the 7mm-08 and 308 Lapua cases.
Good Shooting!!
Kirby Allen(50)