I am going to Aconcagua late in season (late February to early March), and was told to get a -20 degree F sleeping bag. I have a Mountain Hardwear Ultralamina 0 degree bag, and I don't really want to buy an expensive -20 sleeping bag that I might not use much. I have a rectangular 40 degree bag from Golite, and was thinking of using it with the Ultralamina instead of buying a new bag. I also will have synthetic insulated pants, synthetic insulated jacket, powerstretch baselayer, and down parka to sleep in if it were really cold.
Is using two bags a good idea, and Aconcagua is it really necessary with the kit I have? Thanks!