Indeed I am finding that conditions other than fitness CAN make a big difference... so I track which of 3 routes I typically do. That being said, I think headwinds can be the wild-card factor when on the same route.

One of my "routes" is Central Park... where I haven't found much wind to make a difference. When I got back on my bike after 12+ years 2.5 months ago, the best I could manage was about 11.. last Saturday I got 14.1 AND that was from my front door out and back (about .6-.7 from my door to the park).

Oh to be fair, I avoid Harlem Hill, not sure I'm in good enough shape as I have a damaged ticker and take meds that won't let my HR go over 140.