"I use an R1 with the Montbell Alpine Light jacket for temps in the 30's."
Yep, this is the basic configuration that provides the greatest warmth & flexibility. A couple of years ago, Richard N. posted up a clo analysis that concluded that a wind shirt + 100 wt fleece/poly provided the greatest range while active. Add to that the loft/warmth the MB AL provides while inactive (sitting and/or camp chores), and you've got everything from 30-75 degrees covered.
Rather than take both a wind shirt & rain shell, I ended up with the Patagucci Torrentshell pullover to handle double duty along with my polypro LS t-shirt. Of course, it doesn't breath that well, but it serves the dual purpose very well. And at only 10oz, it's very light for the range it provides. In fact, with this set up, I've completely discarded taking any polartec mid, whether it be 100, 200 or 300 wt, since I can use the AL under the shell.
As to down vs syn, I have a syn quilt for its semi fail-safe nature. That is, your last line of defense is the bag – if that goes down, you're pretty much SOL. I figure I can protect the down mid layer with either my shell, or, still being awake, go under a tree/rock. If all else fails, I can always hike out.
With a bag, presumably you're asleep, it's dark/night time, and you're undressed (or in LJs). Since there's no easy way out @ that point, I figure it's worth the slight extra weight/bulk. Of course, that's the point of the quilt in and of itself: to get the weight down a little closer to a comparable down bag while narrowing the comfort range.