Don't own a 338, I did the 300 to 375 route. I would encourage him to build it at a reasonable weight even if he is built like a brick out house. He will get older at some point and a lighter rifle allows carrying more of other things like meat. At higher altitudes every ounce counts and I know of several shots that were blown or not taken because the hunter was winded or breathing so heavily they fogged the scope up.

If it will be used for bear or other potentially dangerous game I like a controlled round feed action but this is not that critical. I think I would do a 9.3x62 before I would do a 338-06 but that is a good one. The 338 will be more readily available and have cheaper dies and it can easily be loaded down to 338-06 levels. But he should get what he wants.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli