A stone built shed with a good tin roof, fire, hot coffee and a dram. !!
If you do go out in such conditions, a good merino wool base layer is your friend. It keeps you skin dry and warm regardless of the level of moisture in the rest of your clothing.
Then have a good wicking layer.
Top layer really depends. Most Scottish hill farmers on the west coast use vinyl.
But if you want a bit more were ability Stony Creek and Ridgeline seem to find a lot of favour with those working in the field. But they are water proof and do cause sweating if you are working hard.
Personally I think the best is to have a a quick drying mid layer, and have a shell type jacket in your pack. If its cold then add a down gilet or jacket into your pack.
When you are powering up the hill and getting hot - let the heat and sweat go. When you stop pop on the warmth, when it rains put on water proof layer. When water proofs are on - slow down and don’t sweat.
If you are with a stalker built like a mountain goat, dressed in a plaid shirt and an old tweed jacket and breeks, don’t even bother trying to outwalk. You will know if its going to be cold and wet cos the buttons on his shirt will be mostly done up. If the jacket is buttoned - ice axe snd crampons will be required.