The higher down quality also have a superior drape. 650 feels like a bag of feathers. My wife and I slept under a down comforter in a duvet for years. After I used a Nunatak quilt for a while I replaced the down comforter with a Jacks'R'Better large quilt. Once you have slept between high thread count Egyptian cotton sheets it is hard to go back to the Wal*Mart specials.
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"In theory, theory and practice are the same. In practice, they are not."
Yogi Berra