For sleeping bag girth, you need to measure your shoulder girth over your arms and while wearing all your insulating clothing (in case the night gets too cold for your sleeping bag).

If you go to a tarp and groundsheet, you'll need a lightweight DWR (Durable Water Repellent) sleeping bag cover to keep rain splash off your sleeping bag. You might be able to skip the groundsheet since most of these covers (aka bivies, but not the kind used without a tarp) have a waterproof bottom. You will need a bug net of some sort in bug season; most of these lightweight bivies like those from Titanium Goat or Mountain Laurel Designs either have a net built in or you can get it put in for extra. If you're going to do the CDT, you'll meet LOTS of bugs! You may find that the weight savings of the above combo over a really lightweight solo tent (SMD Lunar Solo, Gossamer Gear The One, Tarptent Sublite, Contrail, Moment or single Rainbow) are not as much as you think. You might want to look at the most recent entry in lightweight solo "tents," the Z Packs Hexamid, too, which I find intriguing. It's more of a tarp plus bug net, but still fantastically light at 8 oz. plus stakes and ground sheet. Joe of ZPacks also has a link on that page to his Continental Divide Trail gear list which was absurdly small. (I suspect some of us are less tough than others!) Another possibility might be the Six Moon Designs Gatewood Cape plus Serenity Net Tent, which together total about 1 lb., plus the Cape becomes your rain coat. This combo might be a bit too small for you, though.

Have you looked at the Six Moon Designs Starlite pack? With the "optional" (mandatory, IMHO) aluminum stays, it weighs 30 ounces and will support up to 35 lbs. easily. I have carried 37 lbs. in it--my shoulders, back and hips were fine although my knees and feet were screaming! Most of the lighter packs won't support more than 20-25 lbs. I personally require load lifters (which the Starlite has) because my shoulders are very pressure sensitive.

You might want to go over to Backpacking Light and look at the gear lists over there (unlike the articles, they're free, and so are the forum and reader reviews). Caveat--if you're going to get that base weight down to 10 lbs., you really have to cut everything back to the barest essentials. Practice using that minimalist gear a lot under adverse conditions before you commit to a long trip! IMHO, while you don't need spare changes of clothing (except socks), don't compromise on insulation! I presume you've read the articles on the home page of this site; another good source for specific gear items is Mark Verber's website. He keeps up with the latest developments in gear--don't know how he does it!

Re the sleeping pad--the NeoAir may or may not work for you. Sleep styles are almost as individual as footwear! I returned mine to REI because it was not nearly as comfortable and a lot less warm than my POE Insulmat Max Thermo (older version of the Ether Thermo6). With the NeoAir, you need a CCF pad (3/8" to 1/2" is what I'd recommend) to supplement it in temperatures close to or below freezing (without one I got cold below 40*). The POE insulated air pad will take you down to the mid to low 20's. If it's going to be colder, one of those 1/8" Gossamer Gear Thinlight CCF pads would be sufficient supplement for the POE insulated air pad to the mid-teens. The weights (NeoAir plus thicker CCF pad, vs. the POE pad plus thinner CCF pad) will be close to the same. Either will be lighter than your DownMat. You'll have to try all three (preferably in cold temperatures) to see what works for you. Remember that you don't want to blow any air pad up all the way, lest it become brick-like--1/2 to 3/4 full is more like it. Your Mileage May Vary. Remember, though, that a good night's sleep is far, far more important than a few ounces difference in weight!

My Big Four (#4 is my sleeping pad--the above mentioned POE insulated air pad) add up to 5.9 lbs. Of course, I'm smaller than you, which definitely makes a difference for sleeping bag and clothing! On the other hand, I have to have a larger tent (Gossamer Gear Squall Classic, total with stakes 27.3 oz.) to provide a comfortable bug-free space for both me and my 80-lb. dog. Even with that tent weight and a 30 oz. pack, add 7 oz. for a long POE Ether Thermo 6 pad (vs. my short) and 5 oz. more for a long and wider WM Alpenlite bag (vs. my short skinny Ultralite, both 20* bags) and you're still only 12 oz. more for your Big 4 than for mine. If you can use a Gatewood Cape or The One or Hexamid, you'll save significantly over my tent weight and probably make your 12-lb. base weight.

Please let us know how you fare!

EDIT: I mentioned the Tarptent Sublite; I really should have specified the Tarptent Sublite Sil. The Sublite is made of Tyvek which is suitable only for places where it doesn't rain much.