My remedy for an oncoming cold- as much water as you can stand to drink today (flush out time!), hot Chinese food (hot and sour soup works wonders to clear out your head), rest- as in get sleep tonight (early to bed, etc)and lots of Vitamin C.

Is this a ride you can bail out early as in a metric as opposed to the full 100?

See how you feel tomorrow. No sense stressing your body when you're not up to par. Yes, you're conditioned, but 100 miles regardless of hills, etc is no "walk in the park"!