Sorry that I didn't get this post up earlier but due to computer troubles this is the 3rd time I'm typing it out.
Despite my worries that it might not, everything went together perfectly...almost like it was all meant to fit together. The bivy and the overbag are almost the same length. It wasn't even difficult to get each bag inside the other. Good to know in case I need to re-layer in less than ideal conditions.
The overbag has zippers on both sides and robust ties to pull the hood in tight and should really help keep the heat in and the drafts out.
The bundle is bigger now but rolled up it's almost exactly the size of the uncompressed compression bag. Because the compression bag is waterproof AND the bivy is waterproof air gets trapped in the bag so I had to squeeze the air out before sliding the bundle in...a minor inconvenience. The bundle doesn't seem to be too squeezed once it's in there. I should be able to store it in the bag just fine. The North Face recommends storing the Aleutian in it's stuff sack and the compression bag is much bigger than the stuff sack for the Aleutian.
I made a few other changes too. I put the stuff sacks from each of the bags in so that if I need to strip the layers down I can do so in a tidy fashion. I also added my wool long underwear set since they've been designated as sleep wear now. In fact they fit into the stuff sacks perfectly. I can also use the stuff sack(s) as a pillow if needed.
Everything still compresses but it takes a while longer to get the air out of all those layers. I might experiment with leaving some of the side zippers open to help let the air out. The increased tension on the straps make the whole thing wider when compressed and it won't fit into my pack...not yet anyhow. Some playing should take care of that problem.
I weighed the whole thing and it's up to 8.5 lbs. Not bad really when you consider I've added a whole (albeit light) sleeping bag, a shirt and long underwear plus 4 stuff sacks. By my math a sleeping bag (with bivy) that's rated for -30 or colder would cost more, could weigh more (and if it didn't it would REALLY be expensive), and wouldn't be 4 season modular.
If I can fit it into the backpack everything will be perfect.