I use the Carinthia Defence 4 and Carinthia Tropen in combination with a USMSS Gore-Tex bivvy bag, which I find gives massive flexibility - Tropen alone, Tropen with Bivvy, Defence 4 alone, Defence 4 with Bivvy, Tropen inside Defence 4 alone or all in Bivvy for when it gets truly arctic! It could be a lighter less bulky system but for my height 6'5'', it is the warmest , most comfortable system I've ever had.