Some further thoughts on these garments and on windshirts in general.
First, the number of threads asking some variation of do I need a windshirt since this SOTMR went up is impressive. Whether thats an organic demonstration of the utility of windshirts or a testament to market forces, fashion and peer pressure I do not know. Beyond some variation of become a member and read the article d@@@ it I have little to say on the matter. Arguing this is like telling someone why they'll bring damnation upon themselves if they put sugar in coffee; as obvious as it is impossible to explain.
I can only think of one more than day trip in the last 12 months were I didn't bring a windshirt of some kind, and that memory is prominent for deeply regreting not having one. Because they get worn so much, my attention to detail with windshirts is pretty obsessive. Because I use rain jackets relatively infrequently, I'm content with the two I have in the closest and don't pay the market much mind. With windshirts my attention is always on the move.
That being the case, it's worth noting that of the ones reviewed here I've currently divested myself of all but the two Rabs. The Cirrus came back into favor over an unusually warm winter here in Montana for two quite basic reasons: the fit and the quiet fabric. I tried to resculpt the Houdini, whose DWR is better and which dries a bit quicker in use, but the sleeves just couldn't be as well contoured as the Cirrus. This means snow in the cuffs during storms while skiing, and wind freezing my wrists while mountain biking. The Houdini fabric is also really loud, defeningly so with sustained high winds, or while smoking a fireroad on the bike at 30 mph. Not a huge deal, but a regular annoyance.
In short, with the obligations of testing leaving me free to pick whatever I wanted from a huge red pile on the shelf, the Cirrus got the nod 9 times out of 10.
This is a good place to explain the heirarchy of windshells I currently used, primarily based on temperature.
Above 60F is has to be very windy for a windshirt to be needed. In kind conditions like this, when the windshirt will likely stay in the pack and might well be filling the role of emergency rain layer, taking the small and light Cirrus is a no brainer.
From around 35F up to 60F the Boreas over a long or short sleeved baselayer not frequently gets the nod, if wind is the primary concern. The balance of breathability and weather protection works best for me.
If it's a bit colder than that, or light to moderate precip is in the forecast, I'll bring the Cirrus. This is classic spring weather like we're having now, with cool temps, moderate winds, and frequently day-long intermittent drizzle, fog, rain and snow squalls. The Cirrus over the Cap 4 hoody fits the broadest possible range of conditions for staying mobile without stopping to futz with layers.
If it's colder still (25F and below) but calm, I'll go back to the Boreas over the Cap 4, possibly with a sleeveless wool baselayer against the skin. Breathability becomes crucial at colder temps, and the Boreas gets the edge for this reason. The paradox is while the Boreas breaths better while on the move, it dries much slower once stopped. Back sweat can be a bit of a nuisance here, and slowing down for the last half hour before making camp to let things cool down and dry out slowly is a good idea.
If the wind kicks up and/or its darn cold (below 0F) I add a Patagonia Essenshell pullover with a coyote ruff around the hood. The Essenshell is sized to fit over all that other stuff easily, and the fur was a revelation during the 3 trips this winter where it was cold enough to use it.
I also tried and eventually passed along a Rab Alpine jacket. It's a great piece, with full features well executed and a breathability/weather resistance blend between the Cirrus and the Boreas. For many it would work very well. I found it to not quite hit the sweet spot, I was often left wanting one of the other options. The fabric also seemed a bit fragile (the heavier Essenshell is nice for the inevitable bashing through brush which ensues when you ski as badly as I do).
The next windshirt experiment? A Wild Things Tactical windshirt, in the mail as I type. It's 70 denier Epic fabric, and comes in multicam, which was the main motivator. The red of the Cirrus is great for staying visible to your partners while BC skiing, or not getting shot while mountain biking during deer season, but isn't going to get the job done sneaking along alpine ridges after elk. A tougher option withou the heavy fur will be good for bushwacking trips, and I'm curious to see where the Epic fabric comes in on the breathability v/ weather resistance spectrum.