And think of the 338 Lapua, necked up to take 458" bullets!!

Performance, all the fun you can handle 500 gr @ 2400 is no problem, if you like to load to the max, you could probably hit 2500.

As George mentioned, This was done at least 20 years ago using the 404 case, and was called the 460 G&A. Saeed's PH friend Roy Vincent also did a version called the 450 Vincent long.

Not sure about chambering reamers and dies, you may have to dish out some healthy coin for those.

A 338 Lapua necked up would be very similar to the 450 Rigby, which is essentially a beltless 460 Weatherby, which is actually a 416 Rigby case with a belt added.