The best combination for me is a light vest and a light shell. Some combination of these two takes me from freezing to about 60°F, and they both pack light. From 30-40, I use both the vest and the jacket. From 40-50, I just use the shell. From 50-60 I use the vest, and above 60 I pack both and just use a t-shirt.

Last Friday is was 35 for the morning commute, and I rode home in short sleeves and shorts. I totally hear you about the frustration of different needs for the morning and evening commute. To make matters worse for me, most of my morning commute is downhill, which makes most of the evening commute uphill.

If it is expected to be dry (a crapshoot in Portland), I use my vest and my $20 Costco merino wool sweater instead of the shell, simply because the sweater packs better than the shell I use.