The 40 miler almost killed me the other day during the ride. The next day I felt good though so my recovery is good. Tonight or tomorrow morning I am going to start practicing for the 100k by making sure I eat properly before the ride, doing the in-ride things like forcing hydration, regular stops, eating, hanging onto other bikes and letting them full me, etc. Then of course post-ride recovery.
Tonight is 50 miles with proper prep. It will be something to see how I feel between a "properly" prepared 50 miles versus the 40 I did the other night when I went out to do only 20.