For sleeping during race, I take the sage advice that Ethan Passant once gave a tourist at the rafting company we both worked at after he finished racing Tour Divide in 2011: You’re so tired at the end of the day, you could curl up in a flower pot and fall fast asleep. I’ve raced without a sleeping bag and used Reflectix as a pad, but really, trying to sleep without a chamois on in one of those Heat Sheet emergency bivvys in the middle of a wash in Arizona was maybe the most uncomfortable sleeping situation I’ve ever put myself in. But…you’re not meant to be comfortable when you’re racing.
For touring, I take an old 40 degree sleeping bag unless I know it’s going to be really cold, seemingly more for its placebo affect these days any anything. It’s been on more trips than I can count and sure seemed a lot warmer when I first got it for the Colorado Trail Race in 2011. Still, paired with an Adventure Medical Kits SOL bivvy, I can get a decent night sleep down into the mid 40’s and survive into the mid 30s without too much complaint. I do take a full length Big Agnes pad, which I think does a lot.
In a non-race situation, if I knew that I was going to sleep out for more than three to five days in a row, I’d probably opt for a warmer bag, but like food, when given the chance to bank some sleep in a town, I sleep hard and then accept being not 100% rested when out on the trail.