One thing I think is always overlooked when talking about recording guitars loud is the interaction between the speaker and the guitar itself.
I used to love recording my SG on the verge of feedback, and that's one thing you just don't get with any of these setups.
I know not everyone will be looking for this sort of sound/style, but if you are, I came up with a nice solution.
I ran the amp output into a small speaker and tied it to the head of the guitar. You dont need a lot of juice going to the speaker to get the guitar to resonate in a beautiful, controllable feedback manner. It was a delight to play, until the speaker gave up, just needed to give it less beans!