Well, let me clarify something first. One rifle belongs to my brother. The other a good friend. I don't know what their comfort zone is in terms of distance, but once we see what the customized rifle likes, I'm sure my friend will take a poke beyond 400 yards because he killed 2 caribou at 396 and 399 yards with it when it was factory using those 168 TSX loads.
If I had a 300 SAUM, I'd probably play with a 175, 185 VLD, 180 Accubond, and 180 Scirocoo...maybe even a Hornady.
The rifle is capable of cleanly killing an elk at 1000 yards. I suppose if I had one set up the way I would need it to be to accomplish such a long shot, I'd do it.