First does 900 fill have such a significant difference than 800 that its worth shelling out the extra cash. Going to buy 6lbs of down to make three winter under quilts and three winter top quilts full sized my preference. I will design the bag's for a 4+ inch loft to reach into deep temp's. There will be an extra ounce or two but lighter on my wallet. Personal preference I guess anyways. I am looking for the best prices on the market for either 90 or 800 fill down would be absolutely grateful for any links. I have been researching everyday on construction of a awesome quilt. I have experience making quilts and garments and own a good top stitch and serger machine so the difficulty of design is not a factor. I would appreciate your best links on these subjects to add all the numbers and crunch nylon quadrant variables etc. The more information the better will post lots of information and pictures and have more major projects coming. Planning on using down with thru-hiker m-90 for all quilts. Next projects going to be cuben and sil nylon shield tarps.