A R8 is 75.0 inches wide. Almost the same as a Gallardo ( they are based on the same platform after all). I cannot seem to find a good number on how wide the wide body kits for NSX's are since there are so many options.
Looking at the Taitec ones it appears to add about 2 inches to the each so which would make us as wide as a R8. Whats really interesting in that the F355 is also 75 inches wide but the car does not have the same width in the front as the rear. The back is actually much wider than the front which is why when you snap a photo of the F355 and the NSX it looks similar width
Check out the top down view of the F355
You see how its wider at where the back wheels starts? It would be nice if the nsx could do this too, but too bad our freaking front wheels are too narrow to run a even crazier stagger.
Another interesting tidbit is that the Mclaren F1 is almost identical in size to the nsx ( the nsx is actually a few inches longer ). I guess when Gordon Murray wanted to make a everyday usable super car he thought the NSX was the ideal size.