I used that combo a couple of years back and it is an awesome system. If you search through BPL you'll find a bunch of my posts with some good info on it. With no extra down fill, just the stock amount, it's probably rated fairly true from my experience. Any colder then 40*F and you're gonna start to feel it. I had an ounce of extra down in my Skaha and once took the system down to roughly 27*F (-3*C) but had a pair of cocoon pants and down booties on. Another time I was out a bit early in the season and it dipped to about 35*F (2*C) and I had trouble sleeping for a couple of hours. I ended up doing a bunch of crunches to keep warm. Obviously each person is different but I would be surprised if anyone could sleep comfortably at temps approaching freezing. Hope that helps.
Side note: go for an ounce of overfill in each piece of the system. You won't regret it.