I will have to cut and paste all the load standards later, but in a nutshell, the 7x57 pressures for the original 1893 and 1894 Mausers is about the same as for the 7x57R combination guns and drillings. There are not a few old Mausers in the USA, hence the lower loadings of factory ammunition and load data.
As the powders rapidly improved, and Mauser and others built stronger bolt actions, the standards rose. The .275 Rigby, with a 140-gr bullet at 2,800 FPS, was about 260 FPS above the previous velocity for a 139-gr bullet in a 7x57 Mauser. The German Army standard for 1913 was for a lighter 139-gr bullet at 2,740 fps.
SAAMI standards are older and pegged lower than CIP standards.
CIP maximum is 390 MPa = 56,565 PSI = 49,000 CUP.
SAAMI max is 350 MPa = 51,000 PSI = 46,000 CUP.
7x57R is at the older pressure level for the 7x57 Mauser of 41,000 CUP, which is the starting load pressure for the 7x57 Mauser in many manuals.
IMR 4831 is going to fill the case before it gets you into trouble, as it is a bit slow for 140-gr bullets.
IMR 4350 would be better. RL-19 and Norma 204 will do the same.
H-414 / W760 is the go-to powder for accuracy and high velocity, if you want that.
The Richard Lee manual has lots of pressure data, as does the IMR data.
Somewhere around 44.0 gr H-414 and 45.0 gr IMR-4350 will be a plenty safe load in the 2,650 fps range.
But if your rifle has a really fast twist, as old 7mms designed for the 173-gr bullets do, you may find that a longer and heavier bullet will give best accuracy:
Speer 145-gr BTSP, 140-gr SST, 154-gr Hornady are some.
---- PS:
Heym, you are shooting a vintage .275 Rigby, right? If I recall, you said it shot a lot of factory ammunition well, and close to the same point of aim. Which loads are you trying to replicate, and do you know the actual MV?
As I recall, you were having good accuracy in your 7x65R and MV with 51.3 gr of IMR-4831, which would be about the load for 160-gr bullet at 2,530 FPS, a safe load for the 7x65R. The same MV goal for the 7x57 would be good, with the same powder...somewhere around 47.0 gr.