TBPI = 0.500 ... .30-06 Hot Load: (180 gr)x(2800 fps)x(.308 cal)x(.271 Sd) / 84,000

TBPI = 1.00 ... .375 H&H mild load: (300 gr)x(2450 fps)x(.375 cal)x(.305 Sd) / 84,000
TBPI = 1.06 ... .375 H&H hot load: (300 gr)x(2600 fps)x(.375 cal)x(.305 Sd) / 84,000

TBPI = 2.00 ... .458 WinMag SAAMI load: (500 gr)x(2150 fps)x(.458 cal)x(.341 Sd) / 84,000

Just to show how an extra 200 fps of velocity affects the TBPI with same 500-grainer, consider the .458 WM+ at 2350 fps:
TBPI = 2.18

For the 400-gr/ .458-cal bullet: In .45-70 Gov't., .458 WM, .458 WM+, or 460 Wby:

1800 fps TBPI = 1.06
2000 fps TBPI = 1.19
2200 fps TBPI = 1.31
2300 fps TBPI = 1.36
2400 fps TBPI = 1.42
2500 fps TBPI = 1.48
2600 fps TBPI = 1.54
2900 fps TBPI = 1.72

So a .375 H&H is twice a .30-06, and about equal to an Elmer Keith .45-70 Gov't. lever action load.
A SAAMI .458 WinMag 500-grainer is about double the .375 H&H.
Sounds about right. Must be a numerological God wink.

Next will figure a Sir Bob like relation of TBPI to optimum game weight downrange using BC for bullets of
different caliber and same soft point type, like a Woodleigh PPSN for all ...

Ron aka "Rip" for Riflecrank Internationale Permanente
NRA Life Benefactor and Beneficiary
.458 Winchester Magnum, Magnanimous in Victory
THE WALKING DEAD does so remind me of Democrap voters. Donkeypox.