back in the day, I did a century ride in 30F, with the wind chill factor I'm sure it was single digits. It was a miserable ride. Hated it, It cured me of thinking about riding outside in winter. Now my lower limit is 60F. And that is a hard number for me, 59F would be a no-go.
OTOH, there is no upper limit on the temp. In fact the hotter the better. I get excited just thinking about riding in 100+. For me, Triple digits = awesome ride.