Bill,
One thing you haven't mentioned (and I don't know whether your doctor has) is whether your medical team thinks either approach can be equally effective at destroying all of your cancer. In many cases, tumors that are poorly differentiated can't be sufficiently well targeted with IMRT and I believe XRT is still the preferred option in those instances. "Poorly differentiated" means the tumor contains abnormal cells that grow at a more aggressive rate.
Full disclosure: I had XRT at a time when IMRT wasn't even available (and probably would have needed XRT anyway because my tumor fit into the poorly differentiated category). I had pretty severe dry mouth for quite awhile after radiation, but have gotten quite a bit of salivary function back over time with regular use of Salagen, and more recently, regular use of Biotene mouthwash and gel as well.
If you're trying to figure out how much you'll be able to continue working during treatment, I'd advise a good contingency plan. We have a number of people on this site who found they couldn't work at all for awhile once the effects really kicked in, while others were able to keep up some level of work schedule. I went from a normal workweek (pre-cancer) of about 50-60 hours in a client service business to a schedule of about 30 hours a week during treatment and for a number of weeks thereafter.
Cathy