There is no replacement for displacement
If you are going to make the jump from a .375 then go for the 458 Lott or Akley. You can load down to 450 or 400 grn bullets if you want to. The 416 is a step up from the375 no doubt about it. But like the .375 its not quite a big bore and it sounds to me like you want something that will really make an impression on ur next buff. Like you I have shot most of my buff with the .375 but there is a heck of a big diffrence when you thump one with a .458. It's just my opinion, I have nothing bad to say about the 416 and lots of guys love them. Having said all that the .375 is still my favourite and I wouldnt go to Africa without one.