I have a roadster touring with the sport package - got to drive a Nismo the other night to compare.
Engine/exhaust
Was surprised how similar the exhaust note was.
Could not feel any difference in pulling power. I'm sure the Nismo is slightly quicker for the weight advantage but only if side by side.
The Nismo seemed to have less throttle response - when rev'd the revs seemed to hang and not come down as quickly. It was cold out - not sure if that had an effect. Didn't affect my sport model the same.
Handling
The Nismo sat lower and had a great looking stance
The suspension set up on the Nismo was harsh compared to the sport package - can see that it's firmness would be an asset on the track
Other
The seats were a little more spartan on the Nismo and the manual adjustments etc. The heated/cooled and power seats on the Sport model were more refined for sure
The OEM headunit was much more basic in the Nismo
I liked the front clip and rear valence on the Nismo
I liked the rear fog on the Sport
In the end for track use - the Nismo makes complete sense. Preferred the Sport model for street use.
Love them both though.