I really dont think this problem is due to overheating." To me it sounds like a case of hyperhidrosisaka, excessive sweating. For that, youd need to consult a physician and see if there might be a solution such as a prescription-strength antiperspirant.
I might be able to help a little with the clothing-management part of things. For a base layer, Id likely start with what used to be called Patagonia Silkweight Capilene. Now its Capilene 1 (patagonia.com), but its the same stuff: a light, fast-wicking, polyester-based fabric that I find to be one of the more versatile base-layer materials. Polyester absorbs very little water, so it does a good job of pumping moisture to the surface of the garment, where it can evaporate or wick into the next layer. The mens Capilene 1 Crew is an exceedingly useful long-sleeve shirt that sells for $38.
You might also try some wool long underwear. Todays wool apparel is made from very soft merino wool, and I firmly believe its the best base-layer material out there. Its an excellent temperature regulator so it modulates the change from, say, hiking uphill and heating up to hiking downhill and cooling off pretty well. Also, merino wool fibers have tiny little pockets embedded in them. These pockets scoop up water and hold it away from your skin, so your skin feels drier. Its true that wool doesnt dry as quickly as most synthetics, but this is a little bit less of an issue in the case of wool because it retains warmth when damp or even wet. Icebreakers Bodyfit Longsleeve Crew (icebreaker.com) is an excellent midweight wool base layer, and it sells for $70.
As for shells, if youre sweating profusely under a shell, Im inclined to suggest you simply take it off. That applies even if its raining a little; its almost better to let some cooling and evaporation take place even at the expense of getting a little damp. Consider as well a jacket made from eVent, a material thats chemically similar to Gore-Tex but has different properties that in my view make it more breathable. It can be a little hard to find. A company called Ground (groundwear.com) makes an excellent eVent shell called the Repel, which sells for $350.
Hope that helps!
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