I agree with what the others have said based on my long rides. Wiseowl, what has been your longest ride so far this year? I too am going to attempt my first imperial century this year (next month). So far I have 10, or so, 40-50 mile rides, a 70 mile ride and am planning an 80 mile ride later this month. If you can ride 80 miles now in relative comfort I think you should be able to do the full 100. I'd recommend standing every now and then just to keep the blood flowing to the butt area and prevent getting too sore. I've found it helps to count down the miles once you've reached the half-way point. Once you reach 20 miles to go (or whatever your typical ride length is) you know that you only have a normal base ride left. If you can stay comfortable on the bike and stay hydrated and fueled you can do it...at least that is going to be my approach...hope it works.