I'll let you know in a couple of weeks. I just bought one. I was tossing up between it and a Mont, See
viewtopic.php?f=15&t=4043&hilit=Mont+syntheticI ended up going with the Sac 3 because
A) EN rating
B) Price (I got the sac 3 for $170, Mont would have been around $230 or so I think)
C) size, compresses down quite well
Now it may not be as warm as a Mont Extreme, but I've decided I won't be doing any hardcore camping up on the top of a mountain

I was hesitant because it's got a fill which I was having troubles finding info about, but from what I've read one planet are a great brand that stand behind their products (not the Mont isn't of course).
Only time will tell though if I made the right choice!