All the rifles in question are overpowered. The small differences in ballistics between .303 at the bottom of the range and 7.92 at the top of the range are irrelevant - they all possess more than you could ever need when fired from an infantry rifle. British ideal calibre tests came to the conclusion that a 7mm round of intermediate power (.280 British) was ideal.
You’ll note that most of the Western world is now using 5.56mm NATO, which is vastly less powerful than any of the cartridges in question. Also, DerMann, be very careful when discussing FPS. This was a mistake that our dear departed friend liked to make. Muzzle velocity on its own does not indicate the muzzle energy of a projectile. You have to also know the projectile weight.
Snipers using bolt rifles because they are more simple??? Snipers tend to be highly trained and thus the complexity of a weapon is not terribly relevant. They tend to use bolt action rifles because they are more accurate. In the case of WWII sniping rifles, both the German and Russian semi-auto sniping rifles had shorter barrels than their bolt action counterparts, leading to more noise, blast and flash.