I'm having a 30/338 Lapua Imp. done right now. My brother has a 338/378Wby, and I'm having a 338 Lapua Imp. done this fall... these are all on 700 actions.
The reamer I designed has a .405" neck length, suppose to eliminate the throat errosion problems, as the burning powder is redirected from the shoulder angle off the neck, not the throat, and isn't "sandblasting" the throat near as hard. Overheating the throat will still make things relatively worse no matter what, but we'll see how long things last.
S1 likes the Win M-70 for the 338 Lapua size cases, the integral recoil lug does make it simpler for a switch barrel, although the 700's lug can be set up pinned... either or.