There are many, more so that you are looking for a 20degree bag. Do you want Synth or Down? Down there are many options but when it gets wet, its about worthless. But Montbell super spiral deal, or a Marmot Helium quickly come to mind. I just got a Kifaru slick back in 20 and a MOB in 0 which can combine similar to Wiggys, are really lightweight, pack much smaller than my wiggys, but then cost twice as much or more. I have only done a few controlled experiments in the 20 on the patio, but I would say the temp rating is right there where Patrick says it is. I really like the Kifaru compression sacks as well. Cant wait to do a few hikes this spring to really use it out. The 20slick in std width, long lenght, weights 2lbs 2 oz, add 2 1/2 oz for the stuff sack. Weighing it on my kitchen scales shows my setup 1/8 oz over that, so its accurate. Plus its a quick drying synth bag that has many reviews that when back country hunters went to bed wet, the bags wicked the water away and they still slept fine. I already know I am a Kifaru pack/ shelter fan, but their bags are great too in my limited experience.
This weekend if I get time I will compress my Wiggys, 35, 20 and 0 bag and post results if you like, I have been using my first superlight Wiggys for 3 years now and they are still great, but like you stated, heavy/ bulky.
20 slick in small sack on left, 0 MOB in medium sack on right, nalgeen for size.
8man tipi (body only, poles and stakes dont compress), liner, mossy net in med sack on left. Both bags in large stuff sack on right (-35f combo)
