I rode in the same conditions this morning (44F) but just wore a thin long sleeve wool baselayer. I'd have worn a vest but I left it at work. My back and front get wet from sweat when I ride. I have to navigate some narrow pathways on a bridge at high speed and prefer not to have any extra baggage on the side of my bike. I like the wool as it doesn't stink when I get to work so I usually wait for an hour or so before having a shower. By then I've cooled down.