Speed, actual effort, and perceived difficulty didn't really correlate for me.
Donahue Pass was hard because I had stayed up late consuming beer with other hikers at Tuolumne; had picked up my first food shipment; it was my first backpacking trip in 10 years; and it was three days' since sea level that I hit 12,000'. On the other hand I made 18 miles from Tuolumne to Island Pass which was my highest mileage backpacking day in 20 years.
I left Muir Trail Ranch around noon with my heaviest pack of the trip at about 30 pounds. That put me on a hot uphill trail in the afternoon. This was definitely slow but once I hit Evolution Valley it was all forgotten.
For the whole trip I sort of dreaded Forester pass. My plan to make it as easy as possible was to camp at Center Basin Creek the night before. The day before I started very early from Rae Lakes- and made Center Basin by noon. Kept going, made the pass before a thunderstorm and down to Tyndall Creek by 5:00. So I did two planned days' hike, over two passes, and felt great.
I planned (loosely) for my daily mileage to increase as pack got lighter and I got better acclimated- but I also planned only one pass per day in my 15 day schedule which influenced the daily mileages more.
My planning number was 2 mph plus 1 hour per 1000' climbed. Then I plotted out proposed camp spots on the map near a fairly equal daily effort. I seldom camped there- and was happy when I camped past the goal point and a little nervous if I camped before it.
Fastest section? After dropping packs at the JMT/Whitney trail junction a trail buddy and I felt so light, and the Whitney day hikers were moving so slow, that we jogged the next mile. We made the summit in well under an hour- maybe 40 minutes. Compare that to my out-of-shape Whitney climb last April. On snow, carrying a full pack with winter gear and only 36 hours from Sea Level it took me almost four hours from Trail Crest to the summit.