My best was a 4 kill round in The Skeld with 25 second cooldowns. My partner got voted off early for venting before we got any kills. So it stared out 7 on 1 for me tanks to one non imposter rage quit. Luckily, there were a decent amount of tasks, so I played it slow early on and whittled it down to 5 crewmates without anyone suspecting me. But 2 of the 5 had done visuals and the task bar was getting full, so I knew I had to go for it a bit. Hopefully picking off those 2 crewmates who were safe from voting. The round started with me finding someone in the lower corner of shields. Easy kill and a total free kill. No way anyone would find them. Ran around a bit until the cooldown ended and almost immediately found someone in lower engines tucker away in the bottom left corner of the room. Pretty much another free kill. Waited as long as I felt comfortable with before calling an O2 sabotage and making sure to be seen completing it. My next kill was in the hallway as they were heading down toward shields. Doubtful they would have found the body, but I needed the kill anyway and players tend to finish their tasks on the right side first so I figured that was a fairly safe place to leave another corpse. Locked some doors, and ran toward the reactor waiting for the sabotage cooldown to end since a reactor sabotage would win it. But I didn't need to because as I was heading to the reactor, someone was coming down just as the kill cooldown ended and I got them right in front of the last guy.
Even the public lobby appreciated that with more than the generic "gg" comments waiting for the next round. One asked if someone had left the game (since one did after I killed them) and I said that no, I had gotten 4 kills in that round.
Definitely some luck involved getting the first two kills in very out of the way places, but it was still by far my best imposter round ever. Even the game that I was 8 on 1 thanks to my partner quitting and no one else quitting but still won was not as satisfying as that one.