Are you refering to .375 H+H Flanged or belted rimless magnum ?

No the 3 1/4 NE is always the NE, there was a 3 1/4 BPE which preceeded it.

The BPE was loaded in a multitude of loadings, there are some 365 Grains over 120 grains of black and a suggestion that there was a loading as high as 150 grains of black. But the balistics are in the 45-70 class.
It is difficult to compare it to the 45-120 as this is more of a modern myth cartridge than a real item for comparison. It was only made for 3 years, but from data I have on hand it is little better than a 45-70.

Respectfully IMHO if the 450/400 is a shooter to 100 yards, then there is little to be gained by ordering a 30-06/9.3 rifle. There is just too much crossover, the 400 will do all that those will and you just will not have the particular one in you hand at the right time.

I would suggest you carry the sxs and have a good medium (30-06, 8x60/68 ,.318, 9.3,375) mauser with a scope on the truck/trackers shoulder if it is one of those days where everything appears at relativly long range.

Regards