Whichever way the spirit moves you. Either will work fine. I've had four 375 HHs and two 416 Rems. Still have two 375 HHs and two 416 Rems. Hunted with both calibers quite a bit in both North America and Africa. If I had to grab one for Africa right now it'd be one of the 416 Rems in Win M70- the ones I have are absolutely the best, smoothest, most accurate, and most reliable bolt guns I've ever used for hunting. I've had no issues hunting DG or PG with the 416. If I were to choose one of the OP's scope choices for the 416 it would be the 1-6x24, hands down. IMO- Load to about 2350 fps or purchase ammo with... 400 gr A Frame or the Barnes 400 gr TSX or 400 gr TBBC, whichever shoots best and go hunting with no worries.
Just this morning went to the range with one of the Win M70s in 416 Rem to test a load I'd never tried- 350 TSX over H 4895 @ 2500 fps. Been a month or so since shooting one of the 416s and Dang! Forgot how well the stock fits, how smooth the action is, how nice the trigger breaks and how accurate these are! Just under 1/2" circular cluster group @ 50 yds off the bench with the first, cold, clean bore shot in the same cluster! This rifle has a 2.5X Leupold Ultralight.
You forgot to mention the 416 chatfield Taylor (exact same performance as the others using 10 to 30 grains less powder!) I bring both the 375 and 416 to Africa so my son has something to shoot with! Agreed on your scope choices but I'd keep that 375 dialed in for dangerous game in the event your 416 breaks (or vice versa.) Shooting 270 grain bullets from a 375 is quite pleasant so same can effectively be used for longer shots on plains game and surgical shots on Crocs.