Voss has a higher RPM. Krylov and Scar 11 have the same ROF; Lambert and Voss have a higher RPM. They juggle the balance game by changing
Rate OF Fire
Damage
Accuacy
Recoil
Magazine Capacity
Total Rounds (number of mags)
Reload time
If you sit and look at all of the weapons (of comparable levels), such as the assault rifles, and look at their stats side by side, you will find that they really are very balanced. Oh, some are better than others in certain situations. THe stocks are generalized all around pretty good. The unlocks are more specialist.. one is great for CQB, the other is a great long range rifle; but they only are great there.