The only cool night experience I had with my 40deg Prodigy was night where it got down to, I think, 43 degrees. I was wearing boxers and a t-shirt (and no hat) in Tarptent Notch with full net inner, decent breeze blowing through. At some point during night I'm sure I pulled quilt tight around me. Toward coldest at morning I was chilly even that way. Not teeth-chattering chilly but mildly uncomfortable. Not chilly enough that I got out of bed to add more clothing over boxers and t-shirt, though that's probably what I should have done. Drafts not an issue once you pull quilt around you, and at 52" wide (last year's reg size) the quilt was plenty wide for me.
IMO this is entirely expected result at temps close to temperature rating. If I'd been warm at 43deg then I would have considered it a 35 degree quilt. I was chilly and 40deg rating seems about right.
I suspect MLD's 38deg Spirit quilt uses same 4oz Apex as EE 40deg. Here's comfort into that you can get on MLD Spirit page:
"Spirit Quilt 38
38 Degrees : Long sleeve shirt, long pants, socks, light balaclava
32 Degrees : Lightly insulated clothes, thicker balaclava, bivy or enclosed shelter
25 Degrees : More insulated clothes, mo-better balaclava, real nice socks + bivy or enclosed shelter"
Given the comfort into MLD gives for their 28 degree quilt I also suspect the 38deg info is a little optimistic (or alternatively that you should plan on being quite chilly with temps and clothes as described):
"Spirit Quilt 28
28 Degrees: Lightly insulated clothes, thicker balaclava + bivy
20 Degrees : All of the above plus raw animal willpower"