I think 100 feet per mile may be hard but 80+ miles and 100 feet per mile is very hard.
Here is some data from our training ride last Sunday which featured 3X20 minute z3 climbing intervals with standing z4/z5 30 - 60 second intervals every 3 minutes - 43 miles with 4300 feet of climbing with typical grades of 6 to 9% and an average speed of 14.7 mph. To keep the cadence up and z3 power on the climbs, I used my 34/26. I would shift up two to three gears for the standing effort such as a 34/21 or 34/19.
We found that our old Garmin without an altimeter grossly overstated the climbing. For example, this ride would have registered over 125 feet per mile of climbing with our older Garmin.
BTW, the work in Kj directly converts to calories based upon a human body conversion efficiency of 25%. In general, for this type of workout and intensity, I burn around 500 calores per hour.
Entire workout (144 watts):
Duration: 2:56:20
Work: 1519 kJ
TSS: 158.4 (intensity factor 0.734)
Norm Power: 184
Distance: 43.277 mi
Elevation Gain: 4342 ft
Elevation Loss: 4323 ft
Min Max Avg
Power: 0 529 144 watts
Heart Rate: 77 149 121 bpm
Cadence: 13 115 80 rpm
Speed: 0 32 14.7 mph
Altitude: 142 1386 560 ft
Crank Torque: 0 697 164 lb-in