In a video the person got 7 kills in killing overide, he got a total of 680 credits, which is a total of 97 credits per kill. Also a total of 679 xp, one killing spree, a killing spree (+50), and assist (+25). For a total of 86 xp per kill. This is just an estamate.
I think that 680 credits for a decent match sounds reasonable. Keeping in mind that you can get credits in Invasion (I think achievements and unlockables give you credits in the campaign, but I'm not sure). It wouldn't take an overly long time to get the weapons, but at the same time, it wouldn't be exceedingly easy (although good players shouldn't have too much of a problem getting good weapons quickly). Hopefully the Elo matching system sorts that out.