I took the liberty of citing on a space.com message board about Nick's (properly attributed) explanation of gas disk interaction with solids, and eventually got this response from someone who talked to his supervisor working in a related field:

"Gas does orbit more slowly than dust does at a given distance. The reason for this is not gas pressure however. Gas pressure typically acts to thicken the disk, not act radially, and so does nothing to alter the orbit.

Radiation pressure on the other hand, does act radially. The pressure of light upon the gas pushes outwards, partially mitigating the force of gravity. The gas, thus feeling a lower force of gravity, orbits slower at a given distance.

He said the radiation pressure is more of a factor for the gas than the dust. Then pointed me towards some papers that discuss the complicated interactions.

BTW, in case you may be thinking my supervisor isn't qualified to comment (quite possible if you don't know about me) my supervisor is an active quasar researcher with a PHD. In dealing with quasars he basically looks at gas and dust dynamics in accretion disks. A very similar situation. So I'm consulting an expert, not just some guy that checks my paperwork. "