Pulling is somewhat of an art..........you have to know your limits and alway leave enough in reserve to hang on the wheel of the next person who should be a little fresher when you drop off. Boy, have I learned that the hard way. I can ride wheels of really strong riders for a long time- but put me out front while keeping the same pace and I can be toast in no time, especially if you toss in a little grade. I've learned to not drop off the front on a climb unless I have a lot in reserve. Take it to the next crest as it is much easier to grab the next wheel.
For me the the ride is probably appropriately named. I really like rides with a few more hills.......I've done rides in the "flats" and it seems you never get a break from pedaling. Add some headwind and they can be more mentally challenging for me that a hillier ride.
In fact my brother has a really hard time doing longer flatter rides as he has to have position changes to help with the hangovers of a broken hip from getting hit by a car a few years ago. He is fine on climbs but flat give him fits comfort wise.
Sounds like you rode really well Pat-maybe you should think about adding another loop after doing the 100 just for good measure!