Ordered the full Riserva kit (bibs/jersey/arm warmers/socks) and was the most worried about the arm warmers. I have size S arm warmers from Pearl Izumi and they don't stay up. Sugoi's size S works for me and I was wondering if I'd always need to buy Sugio warmers. Fortunately the S/M in these fits lanky arms like mine! I'm 6' tall and these are actually a tiny bit long - they bunch a little at the wrists. No big deal for me, but if you're shorter than me just beware.
These match the bib in that they have the thin fleece layer in them for a little added warmth. I wore these with a very thin wind shell over them on a 40 degree ride and wasn't terribly warm, but fine overall. I'd say these probably work best in 45 - 60.