I am a bit confused. The quality of the Iray Preview render is the same as that of the output for specific settings.
You are talking about a "Final Quality" setting, which I don't see. There is a "Final Render" setting, but that only applies to the iClone native renderer.
Note that the size of the Iray render can be selected to be either determined by the iClone Preview window or by the iClone render size.