my 50-90 with a 550g bullet pushing 1200 in my 12.5#  Sharps is all i care to shoot.but with that load i can let off 50 rounds at the gongs in one session without a "p$#%y" pad on my shoulder and still be smiling.
My buddy likes big African safari cartridges at full throttle. Alot of shooting for him is 10 shots.i hate guns beating me up.

After much searching, I finally located load data.  The first edition of Accurate Reloading's Manual (the red cover).  Bill Falin did much of the work, when not flying fighter jets.
Page 325/6 both have load data for the 50-140.  They developed starting and maximum data by pressure testing a C. Sharps 30" barreled M1874 in 50-140 with a 550gr cast bullet and 140gr of FFg black powder.  It made a pressure of 28,000PSI.

40gr of 5744 made 1466fps.  50gr made 1736fps and 24,800PSI.

The Beast; 105gr of 4350 chronographed 2184fps and 27,500PSI.

Data also included 3100 and 8700 powders.  Since I have all four, it should be interesting next spring.
I get cataract surgery this month, so I will wait a couple months.

Rich