H-414 ( same as W-760) is supposed to be the best powder for the 7x57.
It is very similar to the 4350s ( H, IMR, and AA), RL-17 and Norma 203.
If you have 139/140-gr bullets, start there with H-414. I load 44.0 gr H-414 under Hornady for my 7x57R for 2,650 FPS. In your rifle, 49.0 gr of H-414 or 4350 will give you 2,800+ FPS.
The Speer 145-gr BTSP is a serious long-range bullet which performs at closer ranges, too. I load them in my 7mm-08, .280 Rem and 7x64mm. Very accurate in all of them.
150 gr and 154 gr are good weights, and there are lots of good bullets in that range. You don't need to spend money on "premium" bullets, as the Sierra, Speer and Hornady are very good. If you have not yet bought any bullets, I recommend starting with flat base bullets, as all rifles seem to shoot them well and load workup is easy.
To me, the 173 and 175-gr bullets are a bit heavy, holdovers from the originals. I shoot them because my 7x57R is regulated for them. But if you want a bit more range and punch, the long boattail 150 and 154 bullets are super (BCs of 0.500+), like the Hornady SST and Nosler Accubond. Likewise, in the 160-gr, you have the very tough Speer Grand Slam and Hot Cor, and the Sierra Gameking (0.600+ BC ) in BTSP and BTHP ( tougher).
Use new load data from the powder companies, as many of the classic loads from the 1930s and 1950s are not a safe place to start, and bullets have changed.
----- postscript:
I normally suggest starting with some inexpensive ammo and when you find one that shoots well for the primary game, try to replicate it with your hand loads. But many of the 7x57 ammo is mild, for older 1895 Mausers.
Norma has some hotter ammo, and has a 150-gr with a sort of RN and a 156-gr Oryx RN cartridge, and they sell the bullet for reloading.
You might try RWS, and then try to replicate their mid-weight loads if they shoot well for you.
The discontinued Hornady 154-gr RN have been so accurate in my 7x64, 7x57R, and 7mm-08 that I was thrilled to buy 2 boxes for stash. But the Speer 160-gr in a sort of RN is a great bullet, and cheap. The Hornady 154-gr SPT flat base Interlock would be a do-all bullet for your hunting, and you may find it in their European line of ammunition, which they just don't sell here in the USA.
Reloading Data;
7x57 Mauser; Download pdf
www.norma.cc/en/Ammunition-Academy/Loading-Data/7x57-Mauser
Load Data:
7x57 Mauser Ammunition By
Nosler Inc
Download the page as a PDF
www.nosler.com/nosler-load-data/7x57mm-mauser