Coh2 Stats says:
vet2:
reload weapon modifier 0.71
cooldown weapon modifier 0.71
vet3:
reload weapon modifier 0.71
cooldown weapon modifier 0.71
That means with vet 2 he shoots 30% faster and with vet3 50% faster. (I think... maybe its 60% faster with vet3?

never had a vet 3 Sniper.) And I am not sure if his Rate of Fire is influenced by ready aim time and such things. That could mean that the bonus from the to increased modifiers doesnt translate directly to the Rate of Fire.
Vet3 also gives Armormodifier 2, so I guess he has then 4 Armor?
The Soviet Sniperteam gets exactly the same boni with vet.