How did you go with your tests?
A better test would be to run to empty then fill up with one, run a full tank, then fill up with the other. You will get a much more noticeable difference over a tank. If you don't, well there is your answer. $20 is only about 15l or so you may not notice a difference, even if there is one.
(well technically it would be best to run a few tanks of one, then a few tanks of the other and average them, but lets not nit pick).
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