@Fluteman I will shamefully admit that I own or have previously owned almost every piece of whitetail gear in the Sitka lineup... plus a wide assortment of their big game and waterfowl lines as well. I know a thing or two 'cuz I've worn a thing or two.
Over the past several years I've managed to really dial in my layering game.
Early-Season - down to 45 degrees-ish...
Next to skin: Sitka Core Lightweight pants and tee-shirt
2nd layer Bottom (if below 50): First Lite Kiln 250 longjohns
2nd layer Top: Sitka Fanatic Hoody
3rd layer Top (if below 50): Sitka Celsius Jacket
Pants: Sitka Equinox Pant
Outer layer (if needing windblocker): Sitka Stratus Jacket and Stratus Bibs
Gloves: none or Sitka Fanatic gloves
Hat: ballcap or Sitka Stratus beanie
The beauty of this system is it can cover me in anything from 70-degrees down to the low-40's, just by adding or subtracting a layer here and there. The Equinox pants and the Fanatic hoody are basically worn on every hunt, no matter what. They are staples. The Stratus Jacket and Bibs offer minimal insulation value, but are awesome for blocking the wind. They pack down incredibly well. My normal routine is to walk in and hang my set wearing the Equinox pants, Fanatic hoody, and everything underneath of course. My Stratus set (and sometimes the Celsius jacket) are folded up and attached to my pack. Once I'm settled in my stand, it usually takes 30-60 minutes for me to actually cool down and
need the Stratus layer. Obviously that's when I dawn that outer layer. Which is one reason why I prefer the bibs over the regular Stratus pants... I find that the bibs go on easier and they also prevent any drafts going up your back.
Mid-Season - 45-25 degrees-ish...
Next to skin: Sitka Core Lightweight pants and tee-shirt (not always... only if it's a long walk or there risk of sweat and I need moisture-wicking)
2nd layer Bottom: Sitka Core Heavyweight bottoms
2nd layer Top: Fanatic Hoody
3rd layer Top: Sitka Celsius Jacket
Pants: Sitka Equinox Pant
Outer layer Top: Sitka Fanatic Jacket
Outer layer Bottom: Sitka Stratus bibs or Incinerator bibs
Gloves: Sitka Fanatic gloves
Hat: Sitka Stratus beanie
I do not own the Fanatic bibs because the previous versions were "berbery" down the entire legs and I didn't want the nightmare of burrs, like goldenrod and bidens seeds. The Incinerator bibs are arguably warmer, and waterproof, with a tighter knit that's less prone to accumulating burrs. The new Fanatic bibs are redesigned to help with that problem. Some say the Incinerator line is noisy. Is it noisier than the Fanatic?... Yes. Noisy enough to mean the difference in killing a deer?... Maybe. I haven't had any issues with noise yet.
Late-Season - 25 degrees and under...
Next to skin: First Lite Kiln 250 longjohns or Sitka Core Heavyweight bottoms
2nd layer Bottom: Sitka Gradient pants (these fuggers are a gamechanger... seriously... either worn under waders or while deer hunting)
2nd layer Top: Fanatic Hoody or First Lite Furnace Henley
3rd layer Top: Sitka Celsius Jacket
Outer layer Top: Sitka Incinerator Jacket
Outer layer Bottom: Sitka Incinerator bibs
Gloves: Sitka Fanatic gloves, with Sitka merino liner gloves underneath
Hat: Sitka Stratus beanie or Sitka Fanatic beanie
You DO NOT want to walk any sort of distance while wearing the Fanatic or Incinerator outer layers. You WILL sweat... No way around it. My only bitch about the Fanatic line is that it doesn't pack down very well. It is quite bulky. The Incinerator line is warmer and (somehow) packs down to a more compact and manageable bundle.
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What I have found, Greg, is that while I do prefer a quality baselayer system, I don't personally think the brand or type of baselayer matters as much when you have it paired with HIGH QUALITY mid-layers and outer layers. I can't stress enough how important those outer layers are. The whole trick to being comfortable for long periods on-stand is moisture management and wind management. Insulation is the easy part. It is absolutely essential that you walk in to your spots wearing as little as possible, in order to prevent sweating. Then... give yourself ample time to cool down while in the tree or blind, before putting on your mid- and/or outer layers. Once your body temp is stable and you've got a good insulation system, that outer layer's ability to block the wind really comes into play. At that point, it's simply a matter of ergonomics, fit, pocket layout, zipper layout, etc that makes one piece shine over another. And in my 100% honest opinion, Sitka does that better than anyone else on the market. Kuiu is right up there as well.
I don't want to toot my own horn here, but I pride myself on the amount of time I spend on-stand while I'm out hunting. I don't hunt many days in a given season, but when I do, it's usually during the rut and it's usually at least a 6-8 hour sit... sometimes longer. I've been hunting this way for a long time. Early on in this approach, I would absolutely
suffer through a sit because I was so uncomfortable... usually due to the cold. The past 3 or 4 years I've been building my Sitka regime and it has made an incredible difference. I can honestly say I've never been more comfortable while hunting in extreme conditions than I am currently. I can say that for my deer hunting, my duck hunting, my ice fishing... you name it. A lot of people scoff at Sitka and say it's a waste of money, or that it's not worth it, insinuating that hunters spending that kind of money on gear are foolish. Well, the fact is, those people simply haven't owned any Sitka, or other similar "high-end" garments. And that's totally fine. You certainly don't need to spend that kind of money on "hunting clothes." But me personally, I like to prioritize my money on things that keep my ass comfortable in a treestand or in a duck marsh. It simply makes everything much more enjoyable.
I purchased the fleece vest over the one with "windbreaker" material, because it needs to breath or it'll sweat you real bad. 
