I think the 338 win mag paired with either the 280 Rem or 7MM WSM would be a great two gun battery that would pretty much cover anything that I would ever want to hunt
Well.....I'm close on your heels on that philosophy except for African Dangerous game and then the game starts with a .375 H&H.....but as far as the next lesser powerful rifle I think it's a toss up between the .30-06 and the .280 Remington.
The 7MM Rem Mag is also a splendid cartridge but my leaning for rifle weight reasons is to the 280.....it's a terribly overlooked cartridge.
I'd further agree with the 7mm choice over the .270 options but I think the .280 Remington is a helluva round for most all North American and African plains game hunting.