Their sizing is spot on for me. If you're just barely a size large, you might try medium, because you want it to fit snug. It is very stretchy and does not shrink. You will have no problem returning it if the size is off. In my experience, Rapha has always provided great customer service.

I use their base layers through out the spring and summer season, but for winter I usually opt for my Icebreaker merino wool base (200 weight). It's almost twice the weight of the Rapha gear. It works great from 40 to 60 degrees. Sometimes I'll add the Rapha as a 2nd base layer for additional warmth. The base with a normal SS jersey, wind vest and arm warmers are good for me down to 40. I'm cold natured so I tend to pay extra attention to my options. All the posts on odor free are not exaggerations.

Nothing wrong with the low tech solution. Whenever I feel a wind vest is not warranted, I'll place a sheet of bond paper beneath my jersey as a just in case measure. Easy to discard if not needed.