A critical piece of the puzzle is missing - Viewing distance.
If you are looking at a 16 x 20 print hanging on your wall while sitting on your couch 10 feet away - you would probably could not tell the difference. View it from 2 feet away and you could absolutely tell the difference. If I compare a 16 x 20 print from my 22mp Sinar back to a Print from my 10 Mp D200 at 2 feet the difference is huge ! Granted the tonality is MUCH better with the Digital Back but I am just talking detail here. Hanging on my wall they look pretty much the same detail wise from the couch.
Also - are you shooting at Base ISO ? D200 gets some noise above ISO 400