I would listen to Eric Chan, I believe he is a true expert. Re: “Omit the fleece if you're trying to minimize weight. Fleece is heavy for the insulaton it provides, may 2X or 4X down or synthetic insulation.
To minimize weight have only one base layer.
I have little experience with down, but to minimize weight I would have just down or synthetic garment of thickness required for the temperature you want to tolerate. If you have two, then there's extra layers of inner and outer liner fabrics that are heavy for the warmth they provide - but not that much weight so if you need to wear two garments because you don't have one that's sufficiently lofty, then oh well... In my humble opinion : )”
I’m no expert, but don’t forget this little fleece / non-fleece, A/B scientific experiment done by a mountaineer, and posted elsewhere on this forum:
“My MicroPuff Hoody weighs the same as my R1 Hoody, offers much more warmth, and blocks wind and some rain. If you can take it on and off, it's great. But, if I were to put it under my shell like my R1 Hoody - I'd overheat while moving hard, as it doesn't vent or breathe very well. I went to fleece exclusively after topping out on Shoestring in -10º (before wind-chill) temps, with 30-40 mph gusts. We were working hard and sweating heavily while moving, and my Capilene 3 and R2 fleece let it out. My partner was wearing a MicroPuff inside his shell, and it was a frozen mess, stuck to his shell and not warm at all any more. It breathes, but not nearly as well as the fleece.”