It seems that 5000 is the max for any Campaign challenge, no matter how difficult you make it, still who cares. I love making challenges to myself, something to keep me going.
I hear 2000 is the max for Custom games, any word on that?
I think 2000 probably is the limit as I tried making one for 9001 kills and it would have only awarded 2000 for that so don’t know what else could possibly make it go any higher.