Just be warned, the scores on the boards are being iffy at the moment and it can be a rather frustrating experience.
Recently spent a lot of time getting to 48, and my partner had to leave so we had to call it at that. We both downed ourselves. The high scores saved, but the leaderboard scores didn't. Luckily, my previous highest was only 45 anyway so it wasn't all that drastic a difference, but frustrating all the same.
And it will take a lot more than 4 hours to reach 44, killing 300+ zombies with insane amounts of health per round, utilising an AK-74u (when you inevitably run out of ammo) is very time consuming. I'm always looking for someone who'd be willing to play for long enough to go much higher, so I wouldn't mind playing with you during my days off. :)