With the Visa, 0.42c gives you 0.75 of a point, so double that to give you 0.82c gives you 1.5 points, compared to Amex where 1.45c gives you 1.5 points - costs an extra 0.63c to get the same number of points, so Visa is much cheaper.
FWIW, here are the calcs I did before I paid my ATO bills, just to make sure:
ANZ Q Amex $100k = 150k Q points = 150k Q points ATO cost is 1.45% = $1,450 = 0.96c per point
ANZ Q Visa $100k = 75k Q points = 75k Q points ATO cost is 0.42% = $420 = 0.56c per point.
Having said, that, some people do not have access to large expenses, such as ATO payments, to help earn lots of points and so need more points per dollar spent, so they pay the extra CC surcharge on Amex and get twice as many points as with Visa, at three time the cost, as 0.96c per point is still good value if you want to fly in J or F. Which can make good sense, depending on your situation.
Personally, I do not fly nearly as much as I would like, and usually earn more FF points than I burn, so for me, paying by Visa makes sense, and it is easier in my mind to justify the 1/3 immediate cost of Visa to collect still more points for a potential benefit in the future, and one that could be depreciated at any time...
Hope this helps - please 'like' this post if it did. A little social media experiment - is there anybody out there?!