Rack, I've got both the Renaissance and the North Twin. When I camp in the mountains I use the Renaissance. If I were heading to Grande Cache during sheep season, I'd likely take the North Twin, 'just in case'... I hate being too warm and sleep in Smartwool long underwear. A silk liner supposedly increases the warmth factor by a few degrees, but I've yet to try one. I doubt you'd freeze in long underwear and a liner with the Renaissance, though. Good to -10 for me.
I don't know if ID bags are the ULTIMATE, but for the price they cannot be beat.
Last edited by CDN_DUCKNUT; 04/26/09.