I team the 100w fleece or Polarfleece PowerStretch with insulation like a polyfill vest or pull-over like the Patagonia Micropuff garments.
My favorite combo is a long sleeve silkweight base (Capiliene or Golite C-thru), a 1/2 zip long sleeve Mountain Hardwear Power Stretch Zip tee and a full zip Moonstone Cirrus vest (Thermolite Plus fill), with a Montane LiteSpeed windshirt. I'm using a cape shelter for raingear. A step up for colder weather would be a Patagonia Micropuff pull-over jacket and the windshirt could stay behind. For a rain shell for day hiking or winter coastal hikes, I use a Marmot Precip.
Think of system that will keep the moisture moving and allow multiple combinations. I like light fleece as you can wear it against your skin and it is perfect for sleeping it. The stuff is cheap to buy, easy to maintain and dries fast. I like 200w fleece vests and pullovers on a cold rainy day under a shell, but they work better for day hikes or around town stuff.
UL clothing makes big demands on versatility and multiple use. It took more thinking outside the box for me with clothing than any of the other areas of UL gear. If you are day hiking, you can select your clothing for the activity and season with a resonable survival back-up. Soft shells are marketed heavily (no pun intended), and they work great for skiing, climbing, or travel/commuting, but they are too heavy for the amount of insulation/wind/precipitation protection they provide vs. an equivalent mix of microfleece/polyfill/windshirt. Once you step into multi-day hikes and climate zones from lowland forests to above tree-line, you need a broad spectrum of clothing.
There are microfleece garments that are really more like a heavier base layer, gradually increasing in weight to something like a 100w fleece, and that too keeps increasing on up to a 200w fleece. From everything I've been able to find out, once you start to go to 200w fleece, you mught as well have light down or polyfill garments and you gain wind protection at the same time.
Campmor 200w Polartec pullover: 13.2 oz.
Patagonia Micro Puff pullover: 12.5 oz.
The Micro Puff is easily double the loft, has some wind resistance and DWR too. But the street price is about $100 vs. the Campmor fleece which is just $25. So, for moderate weather, the Campor is a pretty good buy. The Micro Puff is a better on compressibility. I don't have the raw data on insulation for either, but some of the folk here may be able to provide that.
Ratchet down to 100w fleece and expedition weight base layers.
For reference: silkweight GoLite and Patagonia LS tees run 5.5-6oz.
Duofold Varitherm Expedition Weight 360° Stretch Two-Layer LS tee: 7oz.
Patagonia Capeline 4 zip neck tee: 9oz.
Mountain Hardwear Power Stretch zip neck tee: 10oz.
Campmor 100w Microfleece Zip-T Neck: 14oz.
Mountain Hardwear Micro Chill Zip T (100w Polartec): 7oz.
Mountain Hardwear Micro Chill V Neck: 6oz.
Red Ledge Reverse Layer Microfleece Zip-Tee (360g fleece): 11oz.
The figures for the Mountain Hardwear Micro Chill shirts were a surprise to me--- looks great on paper. I really want to get one on a scale!
What I'm missing is the actual loft of each garment. Figures on loft, air permiability, and moisture transport would make choosing these base/intermediate layer garments easier.
All in all the differences are probably small. I'm wondering if the $75 shirts are markedly different than the $20 models.
The other challenge for me was to build a layering system that works in a wide range of temperatures while working hard and still keep me warm in camp and sleeping. It's not very hard to stay warm cross-country skiing, snowshoeing, or hiking up a series of switchbacks, but when you stop, you have a whole different set of needs. I am surprised that the larger manufacturers like Patagonia or Mountain Hardwear don't make coordinated sets of clothing.