"That which does not kill us, makes us stronger"?? Seriously, it is great for the workout, tho it doesn't feel good to be making so little progress with such effort. Reminds me of cycling the tete jaune pass (going west from Jasper, Alberta) It's been a few years, but I still remember how cycling uphill on the pass, into a fierce headwind was a truly disheartening feeling.
Still, it felt pretty good to get to the top of the pass :-)
Good luck wiht your plan to make 120 max miles.