Hey so this is my experience which has led me to rethink a lot of my layering techniques to more in line with the gurus.
The human body sweats for two independent reasons - its is working hard, and because it is cold. The general perception is that you sweat because you are too warm and that you can be too warm due to working hard, but that is not true. You can be in situations where you are sweating due to working hard and still be cold. I don't know the reasons it might be sweating is localised due to local tissue temperature where high-output locations near the liver and near your main muscles are generating the heat and some of it via bloodflow gets around the body but not enough to warm all the body. I've been biking up a hill in a baselayer, there is nil blocking to evaporation but my base is wet from sweat and I'm cold. I've seen sweat evaporate next to skin to recondense on the outside of my baselayer and been wet with nil blockage to that moisture. So I actually see insulation as moving the point that sweat wants to recondense as further away and to protect those parts of the body which can't be heated sufficiently from warm blood from the heat-producing areas. As the core produces much of the heat - it actually needs little insulation when active in cold.
Hence regardless of the temperature if I'm working hard I cannot be wearing any form of shell, and even my windproofs need plenty of venting options and even different type of windproofs.
I've tried varying the thickness of the baselayer for the general temperature, it does not work, because there are times I'm working so hard I do need to be in base + windproof only.
So when its cold I must protect extremities first, hands, feet and sometimes the head in places (ears, face), because regardless of how energetic I am, if its cold enough the warmed blood from the core/muscles has cooled beforehand and besides there isn't enough blood flow anyway to cope with low temps. If I'm walking very fast I've been at 0C / 32F been in just a baselayer t-shirt and had thick footwear and been just-right in that proportion.
For colder, I then need to add a bit of wind protection to the core, and then to the legs. I can be working hard with a thin base, a windproof gilet and a thick foot protection and be comfortable. In some strange way, raising the temperature a little lets the sweat warm enough to be evaporating but it needs a non-blocking layer to do that.
I then need to thicken up the windprotection to the core and move from gilet to jacket
I then add something to the legs. I give leg some insulation before the torso needs, I get sweaty legs and be cold.
This then continues as my needs for insulation increases, I'll add some wicking mid-layer to the torso under windproof, move to thicker insulation on the legs (say windproofs over cycling leg warmers). As output drops for the temperature this then progressivelly all become thicker.
It is only when my output is low or I'm stationary can I be doing anything to block evaporation like put on a waterproof. If I put on a waterproof when high output, even with eVent, it is simply not capable and I get wet from sweat.
There is also a form of sweating which comes from hunger, if due to a need to get to a particular place for a particular time, and if I've misjudged my food needs and I get hungry, there seems a form of sweating due to hungry-effort, somehow like whilst the brain+stomach are shouting "hungry!" the burning of reserve stores (fat?) seems to give off more heat than the burning of my last meal. Anyone seen that effect?
Down whilst active - a thick down jacket has the issue that it can provide a lot of insulation and its very breathable, BUT the re-condensation temperature can end up sufficiently far inside it is recondensing and possibly even freezing. Hence sometimes to move the recondensing point externally I need to layer over it a windproof and tune the mid-layer under the down to not trip me into too-warm which then increases sweat. It has to be VERY cold to wear down active.
There is a huge difference in my insulation needs between active and inactive.
There is a huge difference in my insulation needs been hungry and not-hungry and I begin to feel the cold about 30-40mins before any hint of hunger.