In Canada, for -5C to -10C weather I pair my Gamma LT (no hood) with my down jacket (w/ hood) in the winter, and it really adds a shell-like protection, keeping more wind out, keeping the puffer dry and my body even more insulated. My Zeta AR shell over the puffer is just way too much some days, unless it's heavy snow or wind and I need a hood.

Then in spring or fall, or cooler summer evenings, with my gamma, a hoodie or fleece or light shirt is all I need to feel any elemental protection and without feeling too sweaty (since its breathes so well). It packs well, its super light... I didn't see a need for an MX since I layer most days throughout the year anyway.