Krag ammo is available in 150 and 180 grain. Balistics are about the same. Equal weight will give very similar performance.
The hottest 150 gr 30-40 Krag load I could find gets to 2650 f/sec(@ 39K CUP), with most in the 24-2500 range .... with 1890's metalurgy and a single locking lug, I wouldn't try the hot one.
The fastest Commie Aught Six 150 gr load I've seen claims 3000 f/sec (@50K PSI) , with 28-2900 being more common.
A Krag pushing a 150 gr speer .308 spitzer to 2500f/sec will have a drop of about 18 inches below its 100 yard zero at 300, with 1128 ft/lbs of energy remaining.
A Mosin pushing a 150gr speer .311 spitzer to 2800 will drop 13 inches below its 100 yard zero and have 1551 ft/lbs @300......
13 is "very similar" to 18 only in that they are both numbers in the teens. 18 inches is almost 1/3 more drop than 13......
Likewise, 1128 ft/lbs and 1551 are not "similar" in terms of energy.
By any objective measure (velocity, muzzle energy, retained energy, working pressure limit), the 7.62x54R is more gun than the .30-40 Krag.....
The Krag is just a bit more powerful than the .30/30, and less so than he 300 Savage.
The 7.62x54R is in the .30/06 class, and to say it has "very similar" ballistics to the Krag is just silly.