57 grains should get around 2500.
We can usually predict what velocity a minor change in powder charge will bring by dividing the "new" charge by the old charge, then multiplying the original velocity with the result. Thus 57/59 = .996 x 2590 ("almost" 2600) = 2502.
This formula works very closely with single-based powders, not quite as well with double-based. But it is generally pretty close with minor charge variations.
One thing that may be going on is that all powders do vary somewhat from lot to lot. I went down to Charlie Sisk's shop in Texas a few years ago and we ran a bunch of pressure/velocity tests. One of the rifles we used was my CZ 9.3x62, and we tested some of the loads I normally use. At that time one of these was 62 grains of RL-15 and the 250-grain Nosler Ballistic Tip (now the 250 AccuBond). Everything was identical in the load we tested, except Charlie's lot of RL-15. It took two more grain of powder to equal the velocity I got with my batch of RL-15.
This sort of lot-to-lot variation isn't uncommon. Add that to using a different bullet that might very well create different pressures, and it's no wonder that sometimes data can vary 5 grains or more between different sources of data.
We did confirm, though, that velocity is the best predictor of pressure for the average handloader.