I'm with Quoddy. I have and use the No Sniveler , I like the versatility as I can have or not a foot box , so anything from around 32f ,with some clothing , all the way up to whatever...
I have seen and fiddled with the Arc Alpinist, nice stuff, the Nunatac is a bit more specific, so for some a lighter but as warm or warmer solution.
I also had in mind to use the JRB as a top bag, only tested that in my backyard , but it works.
Dave, don't feel bad, I used to think like that too as I can sort of use my WMs as a quilt, but for warmer weather I do prefer the JRB. Not a big deal, but the hood and the zips get in the way. However I do that with the Ultralite at times.
As with the WM bags, the No Sniveller has continuous baffles, so you can increase or decrease the loft on top .