morebutter, listen to Ethan. He knows what he's talking about.. or call an acoustics consultant.
IMHO a resonant type bass traps with damping in the rear corners would take care of your humps and bumps better than totally killing the room... put some of your home-made diffusers on the back wall.
I have a QRD calculator in Excel spreadsheet and others for download and several other good articles on my web site
(s). Please check out the link to Acoustic Myths on the javakustik
Your room is approximately 1820 cu. ft. and with the dimensions given you have minor modal issues at 50 hz and 173~187 Hz. Never mind the 50Hz but the 173~187Hz can be very annoying.
Suggestion: Take down most of the rigid fiberglass and acoustical cotton that is NOT in the Reflection zone. You can use what you take down to make bass traps in the corners of the room. Use diffusion on the back wall and possibly on the back ceiling. You can checker-board the absorption panels to actually increase their effectiveness while maintaining some semblance of 'natural' sound in the room.
Tip: have a friend help you with a mirror by placing it on the walls & ceiling... until you (sitting in the mix position or listening position) can see the speakers. At that point (where the mirror was when you saw the speakers) place absorptive material thereby creating a reflection-free-zone.
I believe that a good mix room, recording room, or simply listening room should be so enjoyable to be in that you would want to work 12 hours a day in there.