The funny thing I found is that quilts are not necessarily all that much lighter. They need extra coverage on the sides which kind of negates the weight saved by not having a bottom. I wanted to like the quilt option, but when comparing I decided that the Mountain Hardware Phantom 45+ was a better choice for me. The factors that came into play are:

1. It is only one ounce heavier than the lightest Jacks R Better quilt.
2. While the down compressed under you has minimal insulation properties, I don't find the extra warmth to be nonexistent entirely.
3. I liked that the Phantom can be used like a quilt or like a regular mummy bag. The Phantom 45+ is probably roughly comparable to the Shenandoah and weighs pretty close to the same (1 ounce more). I find the ability to use it as a quilt or as a mummy bag to be a plus and for me a fairly substantial one.
4. While listed as a 45+ the EN lower limit is 32 and I have spent a lot of comfortable nights in it at temperatures as low as 18F and did not feel like I was at the limit of the bag with one layer of warmish clothes (bike tights, a light pile shirt, and two pairs of socks).
5. The Jacks R Better Shenandoah was cheaper though by about $100. I figure that the Phantom having a zipper and a hood is more complex to make so a higher price does not seem to be out of order.

I do like the idea of supporting a cottage industry here in the US, but found the Phantom to suit my needs better.

Anyway that is the way the choice went for me and after touring and backpacking some I am very happy with the choice. That said others will have different needs, budgets, and preferences.