I rode in yesterday and my morning commute is done in work clothes. I discovered that 56F is the perfect temperature to bike in long pants and a button, long-sleeved shirt. Cool enough that I didn't overheat, warm enough that I didn't need any excess "stuff".
Riding home it was 60F, which was just about perfect for riding in my kit.
Keep in mind that I've ridden in everything from snow to 100F+, bone-dry and muggy-wet. I do love riding in extreme heat, if it's dry, but that's a special event kind of thing. For my daily, regular riding give me the mid-60s.