It has changed, they've released the GT-501's to the open market in the correct sizes. FWIW, some people are getting 7K miles or more out of the sport demons, and I ended up roasting the 501's in < 4K miles as well, so don't take my own wear as a great prediction of the median wear across all bikes/riders.
There really isn't a gas mileage aspect to motorcycle tires, especially on our bike. The minor differences in rolling resistance, even with reasonable grip differences, doesn't have nearly as much an effect compared to how the bike is being ridden on mileage. We can move the mileage from the 30's to the 60's depending on our throttle hand no matter what tire is mounted. For any particular tire, to make sure it's getting the best mpg, make sure to keep the tire pressures reasonable, and there's nothing else to worry about.
Decent tire mileage thread: --->
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