The link is to one review of both the D70 Nikon and the D200.  I really don't know about the D80.  I am intimately familiar with the D70 and the D200 so those are the ones in the review.

http://www.kenrockwell.com/nikon/d70.htm

I use both the early model D70 and the much newer D200.   The first is about 6 megapixels in full use and the D200 runs about 10megapixels.    With both cameras, I have quite successful prints of the A4 size.  I have to review the European paper sizes to compare with what we generally have in the USA.  : )   I wish we would standardize with your standards!

A4 is 210 x 297mm (8.3 x 11.7 inches approx) and that correlates well with my 8 x 10 inch prints.  I have done only one print in the larger size and from a very outdated Minolta point and shoot.  My "almost" A4 sizes in prints are just fine with no real indication of "digital".  They simply come out as photos..photos...photos.

With careful resizing up if needed, perhaps in 10% increments, you can get larger than expected from less megapixels.

As for the cameras, if price is an issue(and with DSLR it can become pricy!), the D70 version does a credible job and has no probs with 8 X 10 prints, even without resize upward.

Some has to do with the printer..yours or professionally done.  Farmed out professional prints range from the everyday kiosk sort of work to those who recognize color management and have the best possible result.  That can differ widely from outside printer to printer.  As for in-home printng, I simply do not have enough experience with it or the cash, or the time, to set up a printshop in my home.

I  am certain you will get good advice here.  The place is known for the willingness of othere to share, regardless of your equipment or experience.  I learned that soon after joining 'rosity.

Wishing you well.        TomD'Art.