Where or what is YSP?
I would say that a 40F bag isn't warm enough for high altitudes in Summer or even lower altitudes in Spring and Fall many places. Personally I wouldn't consider a rectangular bag, but it is your choice. A 32 F was OK for everything we saw on our XC tour in 2007, but I have been chilly in it at times on other trips.
I usually go with synthetic, but it isn't that hard to keep a down bag dry. I might be more inclined to go with down if my daughter didn't have an allergic reaction when she sleeps in the same tent with one.