Thanks to Australian Rules, we do not have a limit on FF points by Credit Card use. I just used up 7 million miles in the last 6 months and have had (over 5 years) some 38,000,000 miles pass through my account (not to mention a loss of 2 million points when Ansett died).

I got almost 3 million points buying the building my company is in on my Diners Club card (back then it was 1.5 points per dollar) and Diners negotiated a rate of 1.1% (so this was $0.0073 (Aussie) per mile or 0.0037c (US) per mile), quite a good bargin as for AUD$22,000 (US$11,000) I got 3 million miles.