Big Dave, Those quilt ratings are mostly a reference that "this will hold more heat than that"; it is not an absolute, "... you will be comfortable at xx temperature. I'm a warm sleeper and I can tell when the temps get within 10° of the quilt rating. For 40° and above, I'd go with a 30° quilt. But that's just me; some will need more (for the same temperature) some will need less.

So if you can try out some quilts - even unzip a sleeping bag to about 2 ft from the bottom (keeping a "foot box") and use it as a top quilt.

If possible, try out your setup close to home while learning what works and what doesn't. Remember, many weather reports are for the city. Here in Bend, the daily predicted temperature is for in town; it will be colder up towards Mt. Bachelor.

My point is, if it is 42° at night and you are comfortable in a 40° rated quilt - great. But check it before snowshoeing in five miles with predicted new snow.