Last year I spent the night down to 4*F with a Military MSS, both bags inside the bivy cover, and a 3/4 length 1" Thermarest. I had on long johns and a micro fleec pull over. I was good to go, with minor cold shoulders a couple times. I just roll over to warm that side.
So putting a pad with a quilt in my opinion will definitely get you down further. But then again I have used a pad for the last 3 years. YMMV
I just bought a set of 20*F Jacks R Better quilts and gonna go out this weekend to test them out.