Matt in a earlier post you mentioned the 450NE pushes a 480gr bullet at 2050fps, 2150fps is the magic number that regulates most of the older rifles.
ive yet to see a rifle in 450 NE that regulated at 2150fps, most regulate best at around 2050-2100 fps depending on barrel length. also, you will not get 2150fps from a 24" or even a 26" barrel using standard loads. the 500/450 NE tends to operate at even slower velocities of around 2000-2050 fps.
this also goes for the 470 and 500 NE which average 2100 fps.
a heavy bullet of proper diameter at 2000+ fps will do the job just fine. these old cartridges relied on sectional density rather then velocity to kill and proved it works well by the fact that they have been in use for over 100 years.