Can't really answer about the 416 (any flavor) as I've never chrono'ed one. Speculation is that a 350 grain bullet would be fine to 300 yards. (2600 fps, zero at 200y, 9 inches low @ 300y)
.458 Win Mag loads I worked up (400g X bullet @ 2350) still retained 2800 ft/pds (1700 fps) at 300 yards (zero @ 200, 12 inches low at 300y). Looks that would work too.
Couple of things - 300 yards is my max distance, both cartridges produce enough smack to work on game there. The 416 I shot would clover leaf at 200 yards, so accuracy would not be a factor.
Giz