The .338 is my favorite PG round. And were it legal, I wouldn't hesitate to kill a buffalo with it. The issue is the scope; I just could never bring myself to put that much glass on one of mine. So since we are matching a rifle to the scope rather than the other way around, I think you already have the ideal choice - that .300 wby. With that combination, you can go anywhere in the world and hunt anything but the largest DG. And if you have really deep pockets, it would be about perfect for a Marco Polo or Ibex in the Stans. And I guess if you did show up at a Namibian ranch with it, your PH would already be raising an eyebrow over the Weatherby, so you might as well add a 16 power scope and complete his expectations.
Please don't read this as criticism, but I really don't get the high-power variables for 99.9% of the hunting I might do. Such a glass is overkill for any African hunting. In fact the people who I have seen use them, were actually distracted by them - constantly fiddling with power or prallex adjustments (even worse with a trajectory dial or light switch). With the exception of very, very rare applications (that one shot at a Marco Polo at 550 yards), I am convinced most of that stuff is designed to bag hunters' dollars rather than game.