I know you are all set, but this is my thinking also.
The 350 gr TSX worked fine for me in Zimbabwe via 416 Rem M70 and will be what I use when I return. My PH was more than pleased asking upon my arrival. He was using a custom 416 Rigby though with the 400 gr TSX.
I used a 400gr TSX out of 404 Jeffery on my one and only buffalo. That rifle went down the road.
I now have a 416 Remington, and if I make it back for buffalo, I will use the 350gr TSX. Planning on getting out to shoot the 416 for the first time this weekend.