I did the 75k, I felt it a LOT more than I thought I would. I was kinda sick, and had done a ride out to Cambridge the previous weekend so perhaps that played a part - but I think the steady hills and my refusal to go 'slow' made my legs get a good burn on
First time for me, felt great to ride it. Felt awesome to ride in the peleton packs for a bit, too - I wasn't fast enough to keep up with any one group consistently, but I picked them up as they came by me. Hit 37.9mph/60.9km/h on the way down from the Gardiner to the DVP, one hell of a hill + peleton draft
There's a lot of good speed on that highway though.