Wanna talk heavy? I used to have a Super Twin (180W?) with two E120s. Yikes. No wonder I can still pop my shoulders out of the sockets at will. Still have the E120s, though, in vocal monitors. Never loved them for guitar, but I'd try them again.

Speaking of LOUD and CLEAN and OUCH, I had a Peavey Classic (tweed Twin look-alike, but transistor/tube hybrid) with two Celestion Sidewinders (150W per, really efficient, too). Most painful amp I've ever heard, ever. Traded it for a Gibson Les Paul Custom, nice move.

I also had one of these, not sure if this helps you at all, I remember them being difficult to find a while back:

Rocktron Allan Holdsworth Juice Extractor - A speaker to line level signal attenuator. Takes the speaker output of an amplifier and gives you six line level outputs for driving effects, PAs, mixing boards, tape inputs, etc. Has two pre-set speaker frequency response curve settings (one designed by Allan Holdsworth himself) as well as a three band parametric EQ and Rocktron's famous HUSH II noise reduction circuitry.

Marshall also makes the Power Brake:

http://www.amptone.com/marshallpowerbrake.htm

je