Money is no object!

My pick would be the 450/400 3" or 3 1/4", wouldn't make much difference.

The 450/400 is to DR's what the 375 H&H is to bolt action rifles, only a little better in my opinion. ( 400 gr. bullet)

The 450/400 can be built on a smaller frame thus making it lighter and easier to carry all day.

Even though it is lighter than the .500's. .600's and .700's, there is less recoil making it more pleasurable and easier to shoot, thus more accurate for most.

As money is no object, you can have it regulated to the load you desire and can afford to have these loads made for you at your whim. (with all that money you will not have time ro reload anyway as you will be too busy traveling from one hunt to another)