OK Look and ye shall find. I have found some ballistic information myself on the Kreighoff site.

Ballistics for the .500/.416 NE (3 1/4")
(Test barrel 25,5" / 65cm)

PMAX: 39,885 psi (2,750 bar), Copper crusher method
44,962 psi (3,100 bar), Piezzo method

Bullet: Woodleigh softpoint and solid 410 grs (26.6g)

Velocity: 2,330 ft/sec (710m/s)

Energy at muzzle: 4,940 Ft lb (6,700 J)

These characteristics indicate an ideal combination of high energy and flat trajectory. The .500/.416 NE provides maximum effectiveness with moderate pressure. As shown above, velocity and energy are similar to the belted .416 calibers like .416 Rigby, but the .500/.416 NE offers the supreme advantage of a rimmed case suitable for double rifles.

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So from these numbers lets assume the for a 23 1/2 inch barrel the velocity is 2,200 fps with a 410 gr bullet. That would make a 350 gr bullet about 2500 fps and a 300 gr maybe about 2700 fps.

A 300 gr would almost have the same trajectory of a 235 gr .375. Plus a 410 gr .416 bullet at 2200 fps would penetrate pretty well too.

Not bad!