Personally I run very warm. I ALWAYS ware a Pearl Izumi base layer, so I normally have two layers on the top. Even when it is 100 degrees out I have the base layer on, fore it does an amazing job keeping you cool when it is hot and warm when it is cool! I go to a thermal base layer when it drops below 60.
I was out today, it was 64 degrees and I was in my normal summer shorts, base layer top and a long sleeve jersey and was just fine. Yesterday I went out with the wife, it was about 50. I had on the tights over cycling shorts, thermal base layer, long sleeve jersey, and semi thermal outer layer. Again, I was just fine.
I have also cycled in the upper 50's with just shorts but keeping my core very warm and I am very, very happy, too.
I have worn shorts all year around and have go for hour+ walks when it is 20 degrees out in shorts. I have lots and lots of layers on the top with hat and gloves to keep my core warm, and my legs are just fine. I contribute this to the fact that I do run very hot, my legs are a GREAT radiator to help cool down the core if I am waring a bit too much on the core
