North American or Canadian might be the more appropriate term here but I digress..
In my (albeit limited) experience, there is no such thing as a drysuit. The best you can hope for is a reasonably-dry-most-of-the-time-suit. So you should plan on getting damp and possibly miserably wet. Which could suck pretty bad during the boat ride back to shore if you're unlucky or have chosen the wrong underwear.
I suppose I understand what you're getting at but while everyone sweats differently I would argue that one can be reasonably "dry" in a drysuit provided you have good wicking / base layer (as you already stated). Like you, I prefer wool or a synthetic polyester blend as a base layer. As you said there are many different variables such perspiration/sweat, water temperatures, surface air temperatures, drysuit materials, how hard you're working, how long you're on the surface sweating inside your drysuit.
I just hate the misconception that there is no such thing as a drysuit. I would argue that anyone coming out of the water soaked or uncomfortably and miserably damp in drysuit has other issues at hand. I know this is not what you're specifically saying but I've occasionally seen other divers argue that there is no such thing as a "dry" suit without clarifying what they mean.
Myself and dive buddies can dive in 2C-4C water temperatures and provided we have no drysuit malfunctions we all come out of the water reasonably dry beyond usual perspiration and very minor condensation inside drysuit.
To the OP (
@Hal),
40-50 degrees (for me and I suspect others) is a huge temperature range. What I typically wear in 40f (4c) can be very different than what I wear in 50f (10c) water. With that being said, for 50f (10c) water I really like Fourth Element Arctics or DUI 300 gram Polartec undergarments. I wear a single midweight base layer with these and I can do valve drills reasonably well and have good flexibility.
In 40f (4c) or below water, I find these are not sufficient by themselves so I'd wear 450 gram undergarments, or add additional layering, active heated vests, etc. I have much less flexibility here and have to reasonably loft my drysuit in order to get some flexibility back but I can reach my valves.
Of course undergarments and base layers can also highly depend on your planned dive duration / runtimes. I actually wear an old ~8 year old set of Fourth Element Arctics in 72f (22c) water in Florida and some dives I come out of the water freezing.
If you're trying for maximum flexibility then try to limit having multiple layers + additional vest. It can really hinder your flexibility depending on how much room you have in your drysuit or how bulky your additional layers are. If your drysuit is not cut for bulky undergarments (cave cut or well fitting) then you may have issues when you start adding lots of layers.
Obviously everyone's thermal comfort is different but just giving you some perspective.
