I have not personally used QD Cotton Request weight. However, Request is the thinnest weight of their cotton line and I am *sure* it would not have the loft of Hobbs 80/20. The manufacturing process for the two batts is different also, as QD cotton is needlepunched and Hobbs 80/20 is not. QD Blend (70/30) might be closer to Hobbs 80/20, but again I have not actually used the QD so cannot be sure about that.
Edit: Here is a link to the QD cotton website:
http://www.quiltersdreambatting.com/dream-cotton.htm
Although Select weight cotton appears to be closer to Hobbs 80/20 (suitable for both hand and machine quilting), my bet is that it is denser and a lower loft, just because it is needlepunched.