On the FFN server I managed to kill a full 6 people with the sniper shiv.
It was on the 5 point cp map with the glass enclosed final capoint, 2nc cappoint on a spire and middle cappoint on a bridge. Unfortunately the mapname escapes me at the moment.
At any rate the enemy team had the middle point and were trying to push to my team's spire cappoint. I was chasing a spy, and went around to the side with the secondary spawn gate. Once I finally caught the spy I killed him with the shiv and found myself behind the enemy's lines. I was in the wooden building next to the downward slope in front of the spire. I figured I was too close to snipe effectively, and they were moving around too much fighting my team in front of them anyway.
So I channeled Leroy Jenkins and jumped out shiv swinging. The closest opponent to me died in 2 swings, a demoman, never saw me coming. Next I went to the two other snipers, since I was in front of them they were the most likely to see me. Fortunately they were both scoped in. Their razorbacks may protect them from backstabs, but it didn't do a thing against my shiv. The second one didn't even notice when the first died to a crit, and the second died in two swings before he even lowered his scope. Nobody else was coming so I ran forward and killed the medic and his heavy in the same fashion. Afterward, my team counterpushed and took the middle point almost uncontested.
People really need to pay more attention when they start hearing folks dying around them. I don't think I woulda' been able to do that on the DFC server.