You COULD try a McCauley driver in there...a 550 watt liquid cooled driver (rolls off about 2.5K though) - A JBL K120 would give you lots of the clean stuff at full range, as would a PV Black Widow...
(How on Earth do you blow up any speaker other than a Bulldog or P12 in a 40 watt amp?)
If you are really grooving on the original speaker's sound, you may want to just get an extension cab to equally distribute the power load, or another matching amp to get more volume at less power to the drivers...just an idea. Operating your amp at levels to blow up speakers can't be good for any equipment, or your ears. Even just a $79 mic and plugging into the PA could save a LOT of wear and tear on you and your gear.
Y'know, the E120/K120 idea may be the best bet for loud AND clean as you mentioned