I find that when I'm wearing an outer shell, long sleeve jerseys aren't as comfortable as skin hugging arm warmers with short sleeve jerseys. I definitely don't feel as wet.

I'm in Socal, acclimated to warm weather, so my 45F is your 30F.

What I wear at 45F:
1. Short sleeve base layer
2. Short sleeve jersey
3. PI arm warmers
4. Gore convertible (arms can zip off), breathable, windbreaking jacket
5. PI thermal tights
6. Thin skull cap for the ears

The base layer wicks pretty well. The sleeves of the jacket can come off, as can the arm warmers. I often unzip the jacket completely up an extended climb under 12 mph.

And in case you're wondering, it rarely gets to 45F down here. Riding in such "cold" weather requires a late night ride, early morning ride, or a trip to Northern California. Yesterday's daytime high in Socal was 76F.