I used to use 760/414 in the 7x57, and it did provide outstanding velocities with good accuracy--in what might be called normal temperature ranges. But eventually I found it didn't work nearly as well in real cold or heat, proving too erratic.
Eventually, like many people who've posted here, I settled on H4350, which is MUCH more tractable across a wide range of temperatures. But another problem with the 7x57 is that throat length is all over the place in different rifles. I've owned rifles that could take over 50 grains with 140-grain bullets without the slightest sign of distress, and others that couldn't take 47 grains.
Consequently I just advise using enough H4350 to reach a certain velocity level, and leaving it at that. Of course, velocity will vary depending on barrel length, but 50 fps can be added to 24" barrels or subtracted in 20" barrels from the following suggestions for 22" barrels:
Ramshot Hunter also appears to be a pretty good choice, and is a little slower than H4350 so might be capable of more zip, especially since it's a ball powder so more can fit in the case. It certainly works great in the 7mm-08. But I haven't used Hunter enough with all bullet weights to come to a firm conclusion yet--except it's noticeably more consistent in varying temperatures than 760/414, and burns a lot cleaner as well.
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