I think the way Paclite works is that the grey-coloured liner is actually hydrophilic, viz, it sucks up water. You can see this if you rub a small droplet of fluid into the liner with your finger.
On the ground, this seems to mean that it copes very well initially as sweat is simply pulled into the liner, but with sustained high intensity use, the liner absorbs moisture faster than the membrane allows it to escape, with the result that it goes from comfortable to very moist inside quite suddenly.
I think of it as a bit like pouring water fast into a suspended bucket with a hole in the bottom. Initially it's fine, but if you carry on pouring water in at a higher rate than it can escape through the hole in the bottom, eventually it overflows.
In practice, Active Shell is a lot more breathable. To be fair, Gore sell Paclite as an 'emergency shell' rather than as something for sustained high speed use, which is where Active Shell comes in.
Paclite, ime, tears very easily - catch it on a wire fence, for example, and it'll rip with minimal effort. Some of that is down to very fine face fabrics, but some, I think, is the relative weakness of the inner coating, whatever it is. Pro Shell uses tougher face fabrics, but also has a much stronger woven liner.
Active Shell, ime, is somewhere between the two. I know some early proto users reckoned it tore easily, but so far, none of the Active Shell I've used has ripped and with appropriate use - light packs and not dragging it across abrasive rock - it's lasting just fine. It's possible that the new process Gore has used to attach the liner to the membrane and face fabric has in some way reduced tear strength over other similar 3-layer Gore-Tex fabrics, but that's speculation and, for me at least, hasn't been born out in real life.
Active Shell isn't inherently much lighter than Pro Shell by the way, but I think I'm right in saying that some of the lightweight Pro Shell face fabrics are now no longer being used, so lightweight mountaineering shells now tend to be made from Active Shell, with Pro Shell being a little heavier but also more durable. The pay-off is less breathability.
I'm not a huge fan of Paclite for active use. I'd rather pay the price premium and go for Active Shell or lightweight eVent instead and have improved breathability.