From what I understand, the only one who is capping already are those who can do extreme amount of damage on fox, which implies heavy ptw and/or lack of competition in server. It's hardly the norm.
What are you doing on foxes? I'm estimating 20-30m. Like that's common...

that's more than expected, I'm 83 atm, the 80/82 only provided about half. Still, exp cap is a full bar beyond that, 86 -1 exp, so still require huge fox damage to achieve, around 15-20m each time I'd guess.

There are rumors, unconfirmed because I'm lazy amoung other things, that you can get more keys if you burn stamina first. Specifically, the wanted mission is not capped, but the stamina is capped counting the wanted.
There is someone who have reported they got 11 thus far by stamina first.
That said, it is POSSIBLE that wanted mission IS capped, but can go from 9 to 11 (so max per day is 11).
Will have to wait and see... I aint doing wanted until tonight as a result....

Ahem, just recieved reasonable confirmation here:
http://forum.naruto.oasgames.com/en/forum.php?mod=redirect&goto=findpost&ptid=9946&pid=62441&fromuid=27049
That the actual cap might be 11, if you do your wanted missions AFTER getting an ODD number of keys via stamina. FUN