Your comparison is flawed.

If you try to pay with bitcoins, and you don't have enough unspent outputs to use as inputs, you aren't able to even create a transaction.  Any attempt to create a transaction with fake inputs would be rejected by every peer and would never be seen by the merchant at all.

Therefore, bitcoin is again faster since it stops "insufficient funds" transactions before they are ever sent whereas it takes a few seconds for the credit card processor to determine if your card has enough funds.