I personally think that the ring should be small, or not there. What I like about the Asimov is that it looks sleek but still viable, and a ring would remove that. Maybe you could have something like the hab module but thinner, and that spins much faster. Make a hub, and put two of those on the side. It would look something like these two: http://imgur.com/a/ywYPR
They are different and sleeker, and may look cool. I apoligize for the artwork, I did these in two minutes on ms paint