when i started playing zombies. i played town survival with a bunch of newbies and carried my team to lvl 24. i ended up with a reg. skull with 2 tally marks.next game (same map) i played with 2 newbs and 1 guy with the skull and knife + 2 tally marks. the 2 newbs left the game at round 15ish and me and him played till round 32. i had 1000+ kills over 300 head shots. and only had 2 downs. after the game my rank then jumped to a skull + knife and 4 tally marks.
with that being said. i don't think you need 5 tally marks to rank up. i think that its all about your performance.