Just did a 50+ mile ride with 6K climbing with a buddy that is mildly out of shape, but wanted to have an epic day with me. On all the flats I was in low Z2. First long climb (Cat2) starting at the 3 mile mark I kept in the middle of Z3. I decided to hammer a Cat3 climb that came about 24 miles in. I was destroying it, until the road ended due to a landslide and was unpassable. Following Cat2 climb started at mile 42 was done in Z4/Z5. I got an extra bit of climbing at this point, as my buddies legs cracked halfway up the climb. I went back to ride up with him and he ended up zigzagging across the road up the last 2 miles of 11%. Strava nailed his pace at 1.8 MPH (He was on a TT bike as well adding to his suffering). We had a nice long descent that was in Z1, with only a 1/4 mile 12% kicker that I hammered Z5 up and then cruised in to the finish.
I think the key to me being able to hammer up the later climbs were greatly influenced by not hitting the first climb hard, and keeping things under control in the flat sections. I was recovered enough the next day to go back out and smash the first climb of the ride.