I use the stock tank in all my 46s. I use the 82 engine. I can get 13 minute flight times with an ounce or two to spare. You don't want to fly around looking for a place to land. Buzzer goes off at 13 minutes and you land.

I'm not sure the 100 uses any more fuel because you're always only using the bottom end of the power band. I think most are using the stock tank. You'll want to make sure you fully lean down the bottom end on the 100. They come very VERY rich. After a modest break in you can lean it down a lot. That will help greatly with the fuel mileage.

Thanks
Barry