yesterday i tried with a friend and 3 PC's to farm. we did a game wit 1vs2 and ship 40 Kills to try it out! so we did the 40 kills and game finished, but then we all saw the "loading game results" screen for about 10 sec and then we all moved to the lobby and the game didnt show up in the statistic...
So who knows, why it doesnt count?? what do we have to do that it count? do we have to run around with the cows or do we have to shoot? or whats the secret? I hope u guys know that!!!
However, if you want to farm, I suggest you set the timer to "Fifteen minutes".
This will allow you to, in a 1v1, get at best 159 kills (tested ship, Colt pistol headshots, 0 second respawn [no hacks enabled]). If you use a gun and do not repair it, you will get roughly 600 GP, and roughly 700 EXP.
With two players, I would assume that the number would be slightly under double that. Slightly under due to the fact that you have to re-aim every time. I would say 280 for two players (again, with the Colt: some guns allow for dual-headshots e.g. M700).