Last year I used Amex to pay a substantial amount (well over my normal monthly "limit") of taxes in the US. Called Amex in advance and wired the funds to my account. With the credit in the account, the tax payment was promptly processed and my miles credited on the next cycle. I paid 2.49% which I considered a good deal since I use my miles mostly for premium international award travel... so $2,490 buys SFO-FRA/MUC-CDG in LH F, normally an $18,000 ticket.