I wouldn't underestimate the difficulty of the 100 mile route. Having graduated from Penn State, I understand what you mean about the differences between the climbs in central PA vs. the southeastern area. The climbs are not as long, but they can be steep and the cumulative effect takes its toll - especially in the heat and humidity of August. Think of it as the Tour of Flanders with marginally better pavement.
In previous years, people on here have commented that their Garmin measurements of the elevation seem to be significantly higher than what the organizers measure (approximately 7,000+ vs 4,000+, if I remember correctly).
I have finished the 100 mile route in 2008, and the 70 mile route in 2009. In 2008 I had been in the hospital the Friday and Saturday before the ride, and suffering from intestinal jihad on Saturday night. I also got stung on the chest during the ride, and I am allergic to some types of bee stings; fortunately I did not have an allergic reaction. I finished the ride, but I was severely dehydrated and cramping. It was a freakin' death march, and there were a lot of people walking the hills toward the end.
In 2009, I had hip problems in May that forced me in to physical therapy, and to reevaluate my goal. The 70 mile ride was comfortably challenging for me. I finished, and I had a good workout, but it wasn't the sufferfest of the previous year. Obviously my two rides are not an apples to apples comparison due to differing conditions, but the 100 mile ride seems to be significantly more difficult both in terms of the climbing and extra distance.
Based on the description of your rides, I think you'll be able to do the 100 mile route, but I would advise anyone riding it for the first time to ride comfortably during the first 2/3 of the ride, and let it rip at the end if you're still feeling good.