I now use a four layer system similar to what you discussed. Base layer (short or long sleeved), insulation layer, a rainshell, and one more; a windshell.
I was refining this system last weekend. Here's what I recommend, quoting your original post..
1. t-shirt baselayer that is light,and good at wicking persperation
- Outdoor Research M's Sequence T., Merino blend, short sleeved. Merino blends keep the stink down and the polyester dries quicker than pure merino. Get this in a light color for hot days.
2. long sleeved baselayer that is light and good at wicking persperation but is designed to be a bit warmer.
- Montbell MW merino 1/4 zip top, long sleeved. Rationale: Merino feels warmer than poly/blends and reduces flash evaporation. Going uphill pull up the sleeves and unzip, going down drop the sleeves and zip up. Get this in a light color for hot days. If you want poly, Capilene is popular (but not with me).
3. fleece or similar wam layer in long sleeves that is sufficient in ~40 weather.
Down to 40F probably all you need is a windshirt over your base layer.. A windshirt is a windbreaker with breathability; it can be worn when active without retaining condensation. It prevents some conductive and convective heat loss and blocks rain at least until you can put on your shell:
- Patagonia Houdini or 2007 Marmot Ion (not the 2006)
Now your insulation layer..
- REI Woodland fleece jacket, full zip. Rationale, nothing breathes better than fleece, and under the windshell it is quite warm.
- Going colder than 40? bring a Montbell Thermawrap jacket, action jacket, parka, or vest instead of the fleece.
- Going colder than 30? bring both.
When you stop or belay, pull the fleece or thermawrap OVER the windshirt; then re pack it when you move. I recommend dark colors for solar heating.
4. I have a lightweight rain jacket/windbreaker.
OK, but for the benefit of other readers, here are my recommendations.. The windbreaker was re-defined as a windshirt and discussed above. For the rainshell:
- Good: Cheap Gen 1 goretex ECWCS parka from ebay (remove lining)
- Better: The North Face jackets in HyVent fabric, such as the DIAD
- Best: eVENT rain jacket, ex; Integral Designs Thru-Hiker (order one size larger than normal) This one fabric is the exception to needing a winshirt and separate jacket. It is breathable enough to be both (and costs as much).
Of course, all this is what worked for me; I have yet to buy the ID eVENT jacket, everything else I have used and can vouch for.
So with this system you only have 6 items hanging in your closet; short, long, windshirt, fleece, thermawrap, shell. Take four of them and you will have 6 combinations (permutations, really) as the trail conditions change.
Since I'm already rambling; might as well mention bottom layers: Montbell merino long underwear, zip-off REI Summit pants, Montbell UL windpants, Patagonia full-zip Micro Puff pants, and Red Ledge full-zip rain pants.
5 more items hanging in your closet, 6 permutations.
Similar systems for headwear, gloves, and footwear. Closet's starting to get full now..