This is a quote from an online chat I just had with a Discover CSR.

Me: I was wondering what the daily/monthly limits for Money Messenger are based upon? Mine shows 200 per day / 500 per month. I have a friend with higher limits for Money Messenger, even though his spending limit on his card is less than mine.

Discover CSR: I understand your concern with Money Messenger spending limits. I am sorry, however, I can not tell you what goes into the qualifications that make your limits what they are. It is systematic and takes your account, credit history, and use of cards into consideration, though.