That's a good and tough question since "better" is clearly a subjective measure. But given some fundamentals, I think it's fair to say that older Nautilus and CDM series would quite easily outperform current 600 series in overall performance.
This would be primarily due to cabinet construction. My CDM cabinets exhibit a relatively dead response to the old knuckle rap test as compared to my 603s and 601s. They are less resonant and provide a more stable foundation for the drivers. In my experience (and room) the outboard tweeter nacelle in the CDM has a profound affect on soundstage, expecially height.
So while the active components of the newer 600 series incorporates some great trickle down refinement, I believe the design and construction differences found in even the older CDM and Nautilus series to have a more significant impact.
This would be primarily due to cabinet construction. My CDM cabinets exhibit a relatively dead response to the old knuckle rap test as compared to my 603s and 601s. They are less resonant and provide a more stable foundation for the drivers. In my experience (and room) the outboard tweeter nacelle in the CDM has a profound affect on soundstage, expecially height.
So while the active components of the newer 600 series incorporates some great trickle down refinement, I believe the design and construction differences found in even the older CDM and Nautilus series to have a more significant impact.