I'm not sticking up for Norma, but ave. 2000 fps from a 21 inch barrel is probably very close to 2100 in a 24" barrel which is very likely what the load was chronographed in, their catalogue doesn't state this. As you say, why you'd want to fork out Norma's prices for their PH stuff is beyond me, I would think it would be no great trouble to load a 458 Lott to 2150-2200 from a 21" barrel with easy pressures. Their load for the 416/500 is for the 450 gr bullets, not sure what that would do for regulation, one would presume they've checked that in a Kreighoff to be sure.
Steve.