A friend drove my (old, leggy 3.0) NSX last year and said it was the best car he'd ever driven. His current steed was an S8, prior to that he had a 996 - C2 I think, but possibly C4.
I can't comment directly though - would love to drive a 996 or 997 back-to-back "just to be sure"
What I would say is that NSXs are only getting older now, whereas there'll always be some sort of 911 to go back to - so if you fancy scratching this particular itch, I'd suggest sooner rather than later.
"No man with a good car needs to be justified"
Blue '08 FD2 CTR - big, ITR-sized shoes to fill...
Yellow '96 NSX 3.0 - oh was it worth the wait!
Black '99 ITR - well, I had to have another one, the first was so much fun. Miss this one even more than #1...
Blue '03 S2000 - SOLD, flawed but fun
Blue '04 Focus TDCi Sport - SOLD, very good fun for a diesel!
Black '00 ITR - SOLD, still missed
Red '98 Civic VTi - SOLD, probably still bombproof