Winter shell pants

I use Patagonia Simple Guide Pants;

weight: size medium 337g (11.9 oz)
cost: $125.00
colors: black or grey

These are a soft shell type pant with basic features and no reinforcements.

For winter camping I use double layered nylon pants. I've sewn buttons on the inside of the waist for suspenders. (finding light suspenders is difficult. Try dress "braces" instead B/C they are lighter W/ only one strap down the back.) These pants are totally windproof but breath well and, having been washed with Nik Wax waterproofing then sprayed with Revivex DWR, they stay dry in all-day wet snow and light drizzle. I DO use knee high, GTX gaiters with these pants.

For ski patrolling I wear North Face GTX pants W/10" zippered thigh vents that have a mesh gore inside. For them I use only a belt.

Then for REALLY cold weather "out all day" work I use Cabela's GTX pants W/Thinsulate insulation & built in suspenders. I wear polar weight polyester long johns under.

Each pair of pants is heavier than the previous pair.

I am prepared to sew my own suspenders, even for pants that have them. Unfortunately, the overtrousers design with elasticated waist doesn't go too well with them: first, it's usually too low, second, no fly. It's also trickier to sew them in, it would be best.

I use light soft shell pants in spring/autumn, when I don't expect more then knee-deep snow, but for the winter I definitely want something fully waterproof and windproof. My current event salopettes take these conditions brilliantly, but they weight 720 gram. I could probably salvate about 50g by ripping off integral gaiters, but no more.

Patagonia Mixmaster pants would fit your needs – and could be had on their website for a little over 100USD.
That said they are really designed for winter climbing. For X-country skiing I like 100 weight fleece, nylon shell and light gaiters as needed, YMMV.

Alpha LT pants from the bird might be of interest to you.

Ok, Mountain Hardwear seems to come closest at the moment with 380g Pinnacle Pants (plus a cargo pocket!). Is Conduit still the same Entrant as 4 years ago (and same as TNF HyVent) ? Or are they using something better performing now?

There's also fully spec'ed Argon Ice Pants of 4.4oz/m^2 gore pro/performance shell, weighting 450g even with long zipper, zipped off backside, and suspenders.

I can't find MixMaster on patagonia's site now, but google suggests it's a fleece insulated soft shell?

Those Alpha LT pants rock, and their lighter brother Beta LT at 301 gram are also worth considering, but 1.25 EUR/gram is mind blowing.

How do one read those 380NR / 420N Gore Pro Shell fabrics?

No idea, but all I wear on my bottom climbing all winter is the mixmasters, silkweight boxers, maybe a pair of silkweight tights; if it is near freezing and the ice is wet? a pair of Marrmot Pre-Cips, -20C and snowing? I replace the Pre-Cips with Micropuff pants.
Cant say I know too much about WPB bottoms.
Call patagonia, maybe its just not up on their site, they made the mixmasters for about a year but they were a bit of a too technical item (not that many alpine climbers, let alone ones who will pay retail). Moved it to their M.A.R.S. milatery line, I picked up mine off their web specials.
Might not be the very lightest pair – but they'll let you drop carrying a shell, insulation and gaiters for 80-90% of the winter, so I guess its a wash, but like I said YMMY.

I think the Alpha LT would meet your requirements. Also take a look at the Beta AR pants. They are very durable. Lastly the the Beta LT pants might do the trick for you. They weigh in at just 301 grams.

Well for me I use Mammut Champ pant in winter backpacking. They are durable, water / wind resistant, breaths great, stretchy, and the close fit allows me to layer over them.

Now I also ice climb so I’m a bit bias towards these pants but hey, they work great for me!

They are a bit more weight at 550 grams but I love them.