BBF..........I don't happen to have a Lott or Ackley right at this minute and never took photos of the chronograph tapes back when I did have them (I had the Ackley, which for all intents and purposes is the same cartridge) but I chronographed 500 gn Hornady softs and solids from my 602 with a 26" barrel @ 2550 fps..........fireformed W-W 375 brass, I don't recall the load or powder I was using but I had no pressure signs, no sticky bolt lift, no ejector marks, no flattened primers............I have yet to see a 458 WM that would break 2200 with a 500 Horn even from a 26" barrel. Now having said that, I haven't loaded for a 458 in many years, with new powders better velocities may be possible, but there was a good assortment of powders for the 458 even back 30 years ago. Now I also know the Lott is ever so slightly smaller than the Ackley case which was why I was being conservative in saying 200 fps for the Lott case.
You talk apples to apples pressure wise, and I agree, however I chronographed a box of factory yellow box Win 458 from my Ruger #1 which I think had a 24" barrel......anyway, these loads chronographed at 2170 FPS for 5 rounds.........however 3 of the 5, the primer fell out when I opened the action.........factory loaded 500 gn 458 WM.........My point being that if the factory loads them that hot and they still won't top 2200 from a 24" barrel, the odds of us doing it with over the counter powders is about zero..........and my loads in my 450 Ackley were 100% safe and the cases took 5 or more loads and still held primers............I guess I don't really have any PROOF just my experiences, but no chronograph photos or the like, but lots of guys in Whitehorse who shot my 450 Ackley and can attest to what a hellfire, retina detaching, ugly SOB it was.........and it was in a custom stock made for the recoil, large butt cross section and nice and straight with a very open grip, but 93 ft/lbs of free recoil does tend to move one around a little........