I went and looked up an article John Barsness wrote on the 7x57, and he tested three factory loads. The Federal 140gr Partition and Winchester 145gr Power Point both listed at 2660 fps posted higher velocities clocked out of a 21" barrel. The Federal load did 2706fps, and the Winchester did 2666fps. Not too shabby and the Partition is an excellent bullet. Another load to consider is the Hornady Superformance 139gr SST at an advertised 2760fps. I used a handloaded 154gr SST out of my 7x57 and it dropped a large bodied Saskatchewan Whitetail buck with one shot through the lungs. The SST opens up a little explosively so I would only take heart/lungs shot, not go for a shoulder. I would still consider any of the loads from Rem, Federal, Winchester or Hornady before I started spending the time and money to track down a more expensive and harder to find Norma, or RWS load. The Prvi 139gr SP would be great if you could find it, but all I ever turn up is the 173gr.
If you want to store away some 7x57, The Gundealer in MacAdam is advertising 200rds of the Federal 140gr Speer for $279.00 (28 bucks a box is more than what Wholesale is charging out west for it).