Krags are an enduring icon. They may truly be antiques, but definitely retain a large degree of utility in the modern world. "Once a weapon, always a weapon."
With 220 grain cast bullets (and 180's for that matter), I've enjoyed the sweet spot engendered by 16-18 grains 4759 (yeah I have a lot of that discontinued powder on the shelf), and similar charge weights of 2400,4227, and RL-7. Jacketed 180's I only mess with IMR4831 for the little I shoot jacketed stuff in a Krag. 46 grains does it for me with excellent accuracy and safe pressure. If I were to pursue the jacketed stuff in the future I would definitely include 4350 in the mix - lots of load data out there.
The old rule of thumb "back in the day" was 2000fps with a 220, and 2400fps with a 180, using medium burn rate powders. When the .30-40 was becoming long in the tooth at the turn of the century after only around 10 years of service (if you think technology is advancing at a fast pace today it was very similar back then too), Army Ordnance upped the 220 grain service velocity to 2200 fps in an effort to keep the Krag competitive with everybody else. Reports started coming in from the field about locking lugs cracking under the added strain, so they nixed that idea and went back to 2000 fps and life was good again. Modern handloaders would be wise, IMO, to heed that lesson learned the hard way by the ancients. Don't worry, the Krag at that level of performance will still kill anything that needs killing just as well now as it has proven over 130 years of use.
