Lol. Thanks for sharing. Pretty funny.
Are you riding the oil or the LC?
Oil ('06 hexhead). I'm too poor (well, cheap) to afford an LC!
I found two not-quite-consistent fuel requirement stickers on the GS: the EPA compliance sticker on the frame says required fuel is 91 octane (since this is a US government sticker, I assume the unit is average R+M). There's a more prominent sticker wrapped around the fuel filler, and while much of it is worn away it recommends 89 octane. Go figure...
I typically run 89 octane mid-grade. If the station has only 87 octane regular and 91 octane premium, I'll go with the premium. And if all they have (as in Iowa) is 87 octane, I'll take that, with as little alcohol as possible. Can't say I find any difference in performance or mileage between premium and mid-grade. Haven't been forced to run regular all that often, but can't say I find any difference there either, but the bike does sound a little different on regular. If the sound under acceleration on mid and premium is described as a "growl," the sound on regular is more of a "snarl." Subtle but detectable.
As for mileage, with the big square Happy Trails boxes installed, I typically get right around 44-46mpg in normal riding. Blasting the interstate with a full camping load, or riding short hops in late winter cold (30s F) can push it down to about 39, while long, lazy days of non-stop, conservative (45-60mph) riding in the Appalachians can make it just touch 50 mpg.