I think the NSX, assuming HART comes back next year, will likely be somewhat more competitive under next years GT rules structure in the Rolex Series.
This year there were two categories, GT and SGS, next year there will only be GT. The GT class in 2005 will closely resemble the SGS class of 2004 in that the Porsche GT3 Cup Car will be the primary platform off of which the class is structured initially. (so much so that even the Porsche GT3RSR will only be allowed to race with the Cup Car suspension and drivetrain).
If you look at the HART NSX versus the front running SGS cars, thats probably a better picture of where the car will be next year (though you can expect the SGS cars to get marginally quicker as they'll be allowed a few additional modifications, mostly aero in nature).
Brian Bailey