I'm thinking of doing the northern route next year. It actually has less climbing overall than what I just did in Vermont. 25,000ft of climbing spread out over 3,765 miles vs the 30,000ft of climbing I just did over just 300 miles through Vermont.
I'm leaning towards leaving mid May and heading West. I'd get more of the trip done before the scorching hot late July/August months. I'd also edit the route to start in Mass, not Maine.
If I started from the West in Washington State, I'd I have to wait until mid June for the snow to be clear of the mountain passes.
https://ridewithgps.com/routes/48699094