I just did pretty much that (57 and light rain) for a 3 1/2 hour ride. I wore a really thin/fine Ibex t-shirt, arm wamers, a jersey, and knickers. And pretty lightweight socks (not wool). It was ideal for the conditions, for me. I was completely comfortable. It wasn't raining hard enough to require the rain jacket, so I never put it on.
Wearing that base Ibex shirt is a huge help. It's very, very lightweight merino, and keeps my core warm without making it even a little hot. Best thing I ever bought, that shirt.
I like riding and running in exactly this kind of weather. 
PS Come to think of it, this is about the same thing I would have worn had it been 60 and sunny. The only difference is that the Ibex might have come off at some point during the ride--but it also might not have. So maybe what the OP's "guy" said is what works for me--temperature, whether there's sun or not, seems to be what drives it for me.
Last edited by salsabike; 05-02-2009 at 02:59 PM.
"My predominant feeling is one of gratitude. I have loved and been loved;I have been given much and I have given something in return...Above all, I have been a sentient being, a thinking animal, on this beautiful planet, and that in itself has been an enormous privilege and an adventure." O. Sacks