I found the answer on one of my questions:
How warm is the nano puff and down sweater compared to polartec fleece?
http://www.backpackinglight.com/cgi-bin ... gination=1
In short; according to lab measured Iclo the nano puff is equivalent to a polartec 200 and a Pata down pullover is warmer than a 300.
Sounds reasonable to me. Total warmth depends on a lot of factors though.
It's obviously not easy and straightforward to test and I don't know much about Iclo but the test is a good start and seems to give a pretty good estimate. That's good enough for me.
I'm looking at Macpacs Pulsar now. Looks like a really nice one.