I'm an avid backpacker and have found through trial and error that on long treks and keeping my pack at a preferred weight of 20lbs , I'm only good down to 35 degrees, that's with a hammock.
Since going to a hammock i simply can't get comfortable in a tent.
But i will say, the use of a tent will allow much lower temps to be tolerable unless you invest in under quilts.
If funds allow i would invest in quality down, sleeping bag and coat. No man-made material has yet to compare to the warmth to weight ratio of goose down.
Few other things I've learned over the years, eat well and drink plenty of water to stay warm.
I also remember this old saying......it's easier to stay warm then it is to get warm
Hope you enjoy your trip.