I'm thinking about running this game as a speedrun to FC all 85 songs on Expert Guitar, but there doesn't seem to be a category.

well, it seems that the moderators are off about a time haha, didi you try to contact them? i would add, but i only moderate GH 1/WT/DS

added - https://www.speedrun.com/gh5/full_game#Career_-_FGFC