I have pancolitis and when I was at my worst I was going 15+ times a day with lots of urgency. My GI said, however, that someone with just a couple of inches of inflammation could have diarrhea as bad as I did. I never had any pain, though. So no, I don't think you can determine the extent by symptoms.
Symptoms began in November 2008, ~4 weeks after giving birth to my son.
Eased for ~3 weeks in December, possibly b/c of probiotic use?
Returned in January 2009 (with a vengeance), diagnosed with pancolitis on January 30.
Currently taking Asacol (400mg 4 pills 3x daily), Rowasa nightly, Culturelle probiotic, and Zoloft (25 mg).