Its +2 for a kill and -1 for a death. That means you need 50 kills without dying to win. If you ran an even kd and made those same 50 kills you would be at an even 50%. Asuming you get at least 10 kills per match, wich would be on a low end with at least an even kd, you would earn 10% per game, and only need to play ten games at that rate. At aprox 10 minutes per game, thats under two hours, if you only made a 5% increase per game, you would have it done in 20 games. Obviously you are gonna have some good and some horrible games, but thats still not a super long time, during wich you are working on a weekly and daily and can complete some bounties at the same time.