I don't know you definition of "high enough" is, but if the OP has a $5,000 limit he could rack up a lot of miles on the coin deal without a lot of trouble. Sure, you can get them faster at $10K, but the major issue is depositing the coins in large amounts. He could easily turn $10K per month with a $5,000 limit and still have 120,000 miles in a year.