Thanks for Scotty P for getting me off my duff and onto SP.
Here's my take on outer layers for Denali, based on spending way too much time on that mountain since 1994 (17 trips):
You don't NEED an 8000m version for your parka or your pants. The longer cut on an 8000m parka is nice around camp, but they are quite heavy, and are generally overkill, even in early season. I say "generally," because you could make a poor decision and find yourself spending the night out on summit day, wishing you had more gear.
RULE OF THUMB: Don't do "night summits" or push your weather envelope on summit day. Good weather will come, so be patient. Make good decisions down low to set yourself up with a good amount of time to hang out up high and this will set you up for success.
RULE OF THUMB #2: You don't need as a burly a parka, if you have a cook tent. If, between your team, you can save 3 lbs in overall parka weight, you've justified bringing a Megamid-type cook tent. You should bring one anyway, if you're on a not-so-technical route like the W Buttress or the Muldrow.
In my opinion, a Denali parka should have baffled down construction and weigh 1.5 - 2lbs. Anything more is just extra weight. You don't need a DryLoft or waterproof shell, because it won't get wet. You definitely need a hood, but that's about all the standards you should look for. 800 and 650 fill are only indicators of the quality of the down, which will translate into a weight savings for a given warmth of garment, but they are, by themselves, not indicators of how warm a garment is.
Synthetic parkas like the Patagonia DAS will work, but are not as warm for the weight. The new DAS does not have as much loft as the older versions, so the jury's out on it's functionality on Denali.
Pants can be either down or synthetic, but must have full side zippers. Light down like the Volant Pants from Feathered Friends are great, but have them add a zippered fly (if they still don't come with one). A zippered fly allows you to pull your pants on over your harness and clip into your rope through the fly. Though this could be tricky in a rescue situation, the odds are in your favor that you'll appreciate the convenience.
Not all synthetics are equally warm. Patagonia's Puff Ball Pants, Mountain Hardwear's Compressor Pants and Integrated Designs Denali Pants are great, but Outdoor Research's entrant (name escapes me) is too light.
The layers described above will suffice for Denali, 7000m peaks in Asia, Aconcagua, and even Antarctica. You'll want a down suit for 8000m peaks, as you'll be climbing high in the dark, so save your money and get something lighter that will be sufficient and versatile.
It's been my observation that anyone can have an easy trip (or two or three) on Denali, and come away thinking that there's a lot of hype about layers and strategies. Conversely, if you get beat up badly on your one trip, you might come away thinking you need a full-on down suit and 5' pickets to keep your tent tethered to the earth. The above thought are just opinions based on having had plenty of "easy" Denali climbs and a couple of nail biters.
I hope this helps someone.