Michael, I agree that the difficulty managing the down might be a good indicator of loftiness, but the Speer is definitely just as "airy" without quite so much static, float, and cling. It might be more a factor of packaging, the Speer uses a sort of firmer plastic bag while the seven wonders is more "rubbery" plastic if that makes sense, more like what a white trash bag feels like (but both bags are clear, for what it's worth).
Jeremy, in addition to Michael's comments about down source, I can only offer that Speer uses a little certification sticker on the bag from an independent loft tester (I had no idea such an industry existed until starting MYOG down projects). The batch that I got my down from had a "measured" fill rating of 927 c.i. with a "5%-10%" error disclaimer. I posted in a different thread wondering if this would actually make the Speer down that I had "835+" since it's minimum fill rating would be 10% less than the measured 927 value. The Seven Wonders down did not include such data although their website claims that they have independent testing of some sort. I have no idea on the thru-hiker down since I haven't used any yet.
Also, aside from simply Speer's and T-H's community involvement (which probably warrants consideration for most people here) is the fact that you can order other items, fabrics, etc. at the same time.
Regarding shipped amounts, Speer advertises 3.1 ounces shipped and my order measured out to a little over that. The seven wonders ounce that I ordered, while measuring it out last night and stuffing it, came to almost 40 grams. I have no idea if this ratio would be maintained when ordering 3 ounces or if it is a general error range. i.e., if ordering 3 ounces, it seems unlikely that you'd get 40 grams x 3, resulting in a whole extra ounce. More likely you'd get a similar safety barrier to what I got, 3 ounces + 12 or so grams. Or, it's possible that my bag was a case of careless filling and you're as likely to get less than you order as you are more.