Yeah, on realistic servers (and especially these big ones with a lot of players, like Leo's), I feel it is overpowered. It can kill enemies with one shot even on mid+ range and shoots pretty fast, so in a pack of enemies with autos, you can spas them all in a second. Also on realistic, I like that every spas shot behind me is speeding me up, so I can get to mid range enemies quickly.
But for m79/chainsaw player, like me, it is hell to play against spas users, since they shoot so fast.. So I would take firerate a bit down [just on realistic servers].