Sometimes i use a bivvy-bag, sometimes i don't. Depends on the conditions, and wether i'm in a tent or a tarp.
Depending on temps, i'll wear a hat or my Nunatak Skaha Plus down pullover. As someone said above, with a seperate hood/hat, you don't end up with a face full of sleeping bag hood when you turn over.
I love the quilt and have been toasty down to about -3C this year in a tent. I think it will do me for a lot lower temps.
I would need more insulation under a tarp, i think. That's why i e-mailed PHD. I would like a warmer quilt, made to my specs. The exchange rate has made it prohibitive to go back to Nunatak at this moment in time! :)