Two quick comments:
1) I know a guy with a Boss GT8. And he swears by a Nobles OD in front of it. Amazing tone always.
2) A speakers output may change a lot at loud volumes. The speaker will go into mechanical compression (ie have trouble moving back and forth linearly for the volume). So you get some compression and a mid boost, I think, when the speaker is driven. May sound thicker, more present, and be more responsive to touch. Or you can have it too loud and it sounds like crap, but will ascend you to Valhalla