Jason, I think people over estimate the impact equipment has on sleeping comfortably and underestimate the impact skill, technique, and ones body make up. I have been putting considerable thought into this as the last several trips I have taken with a friend he struggles through the night while I tend to sleep fine. We are similar in age, weight, and condition. One night in particular was really brutal on him.
To answer your question I would say yes you should have been able to stay absolutely toasty in the gear you describe. One thing to consider, how sure are you the low was 20 degrees. Could it have been colder?
Assuming the low was indeed 20 degrees lets consider what can impact comfort
your body's natural ability to deal with cold (cold natured, hot natured, etc)
your body's current condition when going to bed (tired, wet, hungry, thirsty, etc)
insulative items (quilt, jacket, balaclava, etc)
ground insulation (mat, pads, etc)
sleeping position (back, side, stomach, etc)
sleeping technique (head inside quilt, quilt tucked under mat, etc)
Here are my thoughts. My coldest night "under me" was in a shelter. I suspect the plywood floor quickly lowers in temp as the air temp lowers. You might be better off sleeping on the ground which can provide natural insulation and is buffered from extreme temp swings. Just a theory. I know a lot of folks use neo air, but I am suspicious of sleeping on air, especially when the temp is below freezing. I've had great luck with foam pads but 1/8" does do much. For those temps I find a 3/4 length GG nightlight pad to work like a champ. And it weighs 10 oz before trimming. Mine is just over 6 oz.
Consider your condition. Make sure you are well hydrated before going to bed. Make sure you eat something hot for dinner. I also have a cup of hot tea right before turning in. I also find it best to hike right close to the time I will camp. Before going to bed you might want to take a quick walk or do a champ chore like gather fire wood.
Consider your position. I believe sleeping on your back is the most efficient. It took me a year to train myself to be able to sleep on my back (just for this purpose), but now I can do it just fine.
Consider your quilt use technique. First it is critical the quilt wraps under you. I know some disagree, but I think it is best to not wrap the quilt under the pad. Wrap it under you with the pad beneath. JRB quilt don't come with under straps, but they do have loops that make it easy to add. The lighest is to simply use shock cord with a couple of cord locks to make them adjustable. I was also have you consider using a 7-8 oz bivy with breathable top. MLD superlight, ti goat bivy, BPL new vapr bivy, etc. Until you learn how to sleep and seal off the quilt a bivy will help reduce heat loss from gaps and wind.
DO NOT pull the bag over your head. Your moisture will go into the bag in dampen the down resulting in loss in insulative ability. Keep your head out, cover your head with a balaclava (walmart sells for 5 bucks) or better yet use a down one from Katabalic.
I'm at a loss for your feet. They should have been fine. I'm guessing its just a function of your core temp not being maintained and thus the first place your body draws heat away from is the extremities. I only sleep in a single pair of socks in this temp. I use a MYOG quilt with nearly identicial dimensions to yours but weighs significaly less 20 oz.
Hope this helps,