Hi everyone, just a report back. I did the Northern Tier in 48 days -- 43 days of riding and five days off. I had planned on 40 days of riding and three days off, so not way different than my original plan. My overall average was about 100 miles a day.
I had planned to do 100 miles a day every day through Washington and western Montana, but that turned out to be too much. I could only do one mountain pass a day, and the days that I did do 100 miles out west, it was really tough. I was on a loaded recumbent that climbs pretty slowly. And until North Dakota, every road is chip seal, which slowed me down quite a bit.
It was also super hot. I avoided the worst of the NW heat wave, but it was mid-to-high 90s all the way through Washington, Idaho, and Montana. At least in Montana, that's quite a bit hotter than usual. I had to take off three days in Great Falls to avoid 100+ temps in some remote areas of eastern Montana.
For the ~3000 miles after Great Falls, it was fine. I worked something out with my boss so I could work a little along the way, which made my end date a little more flexible. I did 100-135 most days from Great Falls to Bar Harbor, unless there was heavy rain or I met up with friends/family.
I'll say that doing the trip in 48 days was only possible because I took a recumbent (a well-used second-hand Bacchetta). I didn't have any issues with saddle sores or hand, neck, or back pain. The recumbent is a bit slower (especially climbing), but I was able to do 14 hour days and never really needed any recovery time. I just rode slow and steady all day.
Thanks for all the advice and encouragement. Washington and western Montana really felt like a reality check, and I look back at my original itinerary with some humility. But 100 a day on the Northern Tier is possible! And I really enjoyed it!