I've taken my Caribou with a silk liner to 28-30F a few times and was fine. In fact just two years ago at Vidette Meadow it was 30 or so, I had no issues and I was 57 at the time. I go with the theory that cold air sinks. Looks like you have plenty of clothes to add in the wee hours of the morning to stay warm. Once I get a movin in the morning, I'm fine. I've also found that sleeping out in the open is cooler, you at least need something to cut the wind. Up north here, not much snow left, the road is open into Bucks Lake on the Plumas NF and that can be a struggle sometimes to be open by Mother's Day or opening of fishing season, end of April.
I live up north a few miles from the Bucks Lake Wilderness, so it has been nice the last few years as I collect stoves and I'm getting out a whole lot more.