50-something in Mars War.
I was the gunner in a 2-person tank. Our driver took us right up to the front door of an enemy watchtower that had a respawn point inside of it. I got about 20 kills before bailing out just before the tank exploded.
I ran backwards away from the tower, sniping anyone who peeked their head out, until I found some terrain that would block line-of-sight. Once I was hidden, I worked my way to a hill that overlooked that same tower and resumed sniping until I ran out of ammo.
The match ended before I could re-arm.
A different match had a lower count kill-streak, but it was more fun to pull off.
I was the first person to spawn on my team, and immediately jumped into a jet from our 1 starting base and after-burned over to the opposing team's 1 starting base. I bailed out over the back door, sprinted to the base's generator and blew it up (meaning they can't respawn in that base anymore). Since the match had only just started, the other side didn't have a 2nd base to spawn into - if I could prevent the people who had already spawned into the match from repairing the generator, my side would take over the map with no resistance. I lined the hallway leading from the respawn room to the generator with hidden remote explosives, and killed the first 4 engineers to respond as they came around corners and passed boxes. I crouched behind boxes, and stood still in alcoves along the hallway, letting enemies pass by me in their haste to repair the generator, then popped out and shot them in the back.
The few opposing players left in the map trickled by me in 1's, 2's, and 3's and I held them all off single-handedly, winning the match before it ever really began with a 17-0 kill streak.