Like many here I have been trying to work out how to rank up after being stuck on skull for months.
I decided to create a second account and behold after two weeks and making use of the guide L8Down has provided I have ranked up to Dagger.
Agree with Pentagon Thief regarding the ratio being moved up or down depending on the situation. I think there is a set formula but but the threshold to rank up is different for each player i.e. it depends on how well you've gone in the past 'X' games and other factors that are obscure to us.
I do not think high rounds are a critical requirement to rank up (well at least for Dagger) because the highest I ever got was 23. Just consistency and improvement over time is the key.
Here are my stats to help those out there who are still working things out. By listing my stats at the end of the round where I rank up...at least hopefullly there is something for you statisticians out there to correlate.
Crossbones
Kills: 1478 Bullets Fired: 10094 Downs: 11 Revives: 46 Grenade Kills: 43 Headshots: 482 Deaths: 6 Gibs: 1439 Perks Drank: 30 Doors: 9 Hits: 7431 Miles Traveled: 20 Kills/Down: 134.36
Skull
Kills: 2775 Bullets Fired: 17886 Downs: 19 Revives: 62 Grenade Kills: 88 Headshots: 482 Deaths: 12 Gibs: 2625 Perks Drank: 44 Doors: 27 Hits: 14622 Miles Traveled: 35 Kills/Down: 146.05
Dagger
Kills: 8587 Bullets Fired: 51131 Downs: 47 Revives: 132 Grenade Kills: 317 Headshots: 2766 Deaths: 32 Gibs: 8305 Perks Drank: 120 Doors: 66 Hits: 42748 Miles Traveled: 82 Kills/Down: 182.70
Special thanks to L8Down for starting this thread and the time in putting together all this useful data which I used as a guide to rank up.