I have an EE quilt. It's rated at 20*F with 30% overfill. This past weekend I had it in temps around 15*F and wore only my thick winter base layers (no puffy clothing except a down hood) and was warm. I think with extra clothing I could take this quilt into the single digits. Actually, now that I think about it, I originally went to bed with my puffy on and some insulating pants. I woke up during the night because I was way too hot and stripped down to my base layers. Was comfy till morning.
I've also had this quilt in the 40's 50's and 60's. Overkill? Maybe, especially when you could get away with a lighter quilt at those temps, but this quilt can adapt!
Tim uses something called Karo baffles. Basically, the baffle chambers are not totally separated from one another, allowing the down to shift. Normally this is undesirable, but not in this case. The down mostly stays put until you *want* it to move. Then it is quite easy to shift the down around.
If I lay my quilt flat, I can shift nearly all the down (or as much as I want) directly to the center in less than 30 seconds simply by patting the edges. This pushes the down into the center baffles, making it a warmer quilt for colder temps. Conversely, if it is a warmer night, I can pat the center of the quilt, forcing the down out to the edges, again in about 30 seconds. This means there is less down directly over me, making the quilt not so hot.
You also have the options to zip up and cinch down the footbox or lay the quilt flat for more venting to tailor it to the temps you are experiencing.
The argument can easily be made that getting two quilts designed for their respective temp ranges is more practical, but if you want or can only afford ONE quilt to do it all, I highly recommend an Enlightened Equipment quilt. For 24 ounces, I have a 4 season quilt, and its versatility makes it one of my favorite pieces of gear.
P.S. I think the 30% overfill option actually keeps the down in place better since the quilt is more "full," making it harder for the down to shift around on its own.
P.P.S If you need special sizing, talk to Tim. He was great to work with. I'm 5'11", 170lbs and I have the 6' foot regular size quilt. Fits me well.