You favor the Paramo over the traditional Buffalo? (I know that the two systems use totally different methods but they seem to be the Big Two in the UK.
I sometimes also use a Montane Epic Jacket (no longer made), which is about half the thickness of my other Montane PP jacket, the Extreme Smock. I'm not in the UK, (Japan) so the weather conditions are a little different here... it rains just as much, but in torrents rather than long, non-stop drizzles. I like both PP jackets, but they are very bulky (often end up walking just in my base layer even in the winter, and so putting them away in the pack takes up too much room) and way too warm most of the time.
With the Paramo you get a completely waterproof system that is more breathable than anything else on the market, even Barbour wax jackets. I think a lot of people tend to continue to think in conventional terms when using them and so misunderstand them as being too heavy. I think it is more accurate to see them as waterproof "mid-layers" that can act as outer layers, effectively getting rid of the need for an out layer. If you bring a windbreaker, too, you have a system that can handle light precipitation and be very light, or you can use the Paramo on its own and be a little warmer, or both, to get a little warmer still. You can also wear them directly against the skin, just like PP clothing, and they will do the same thing (except they are not as warm). The Velez Adventure Trousers are the only thing you need in cooler weather. For late Autumn/ Winter trips you will never take them off. I usually find that Paramo is just right in most rain conditions, because the rain cools everything down, and Paramo never gets moisture buildup inside, even when you're sweating profusely. The only time I take them off in the rain is when it is really hot... then I just don't need any rain layer at all, as long as I can dry out quickly during breaks (which Paramo is also good for... they will dry out your clothing faster when you take a break and put them on over your wet under layers... as will Pertex/Pile systems. Goretex just can't do this).
Unlike PP systems, too, you don't have to wear them against the skin for best results. Just wear a regular layer underneath. Or a fleece or fiber-fill insulation. The system still works (it doesn't depend on body heat to transfer the moisture, unlike PP clothing).
However, if you do a lot of bushwhacking or climbing amidst rocks and there is a high chance of abrasion, your Buffalos will be much more durable and resistant to ripping.
I am very interested in the new Fuera Ascent Windproof and Summit Hoodie. I'm think that I can get by with my Montane Lightspeed in lieu of the Windproof and just use the Summit Hoodie underneath, effectively making a near fully waterproof system that is very versatile.
Paramo for insulation, for day hikes maybe, but the weight is just too much for backpacking. Fleece, down, synthetic fill, all do the same for less weight.
Julian, yeah, I kept eyeing the Paramo insulation, but the weight is prohibitive. What do you think of the system if you use it like a PP system, during winter, when you never take the clothing off?
For the Velez Adventure Light Smock, I may just end up sewing a half-moon shaped flap of silnlyon along the front portion of the hem, to get more waterproof coverage.