Lets keep it friendly moto..., as I said I may have gotten a little off topic - and for that matter the OP wasn't talking about 13 x 19 prints . I am actually agreeing with you on the 6 mp vs 12 mp example as I have both as well.....unless you have your face right upto a print they look pretty much the same at that size. I guess if we look at the original poster thought on native resolution ie: downsize the D800 to the same size as a d200 native resolution will the print look any better from the D800. ..... So back to the original question ....not sure how much of a difference you would see...love to see some samples though.
P.s I looked at your site moto ....great work ...I am close to the housatonic river, fished there many times !