Daryl,
When talking about large bore big game cartridges of .400 cal and larger, 55,000psi to 63,000psi are bolt gun or single shot pressures, not double rifle pressures.
We are dealing with the 500-416 NE here, which is a flanged cartridge designed for use in double rifles, and intended to produce similar performance to the .416 Rigby.
Once you get into the large bore double rifle NE cartridges, pressures of 55,000psi to 63,000psi are unheard of. They just don't exist, and for good reason.
With large bore Flanged NE cartridges, here is an idea what you are dealing with.

450-400 3" NE.....41,000psi
450-400 3.25 NE...43,000psi
450 NE 3.25.......44,000psi
450 No2 NE........41,000psi
500-465 NE........36,000psi
470 NE............39,000psi
475 No2 NE........40,000psi
500 3" NE.........41,000psi
577 3" NE.........36,000psi

Notice that none of those cartridges are rated at anywhere near 55,000psi to 63,000psi.
You can also see that none of those cartridges are rated as high as the 46,000psi of the 500-416.
The 500-416 NE is a double rifle cartridge, and is definately not one of the lowest pressure big bore flanged NE cartridges which were designed for use in DR's.
It is actually one of the highest.

Please note that I am not saying that there is anything "wrong" with the 500-416.