As final products, there is no practical difference between a jpeg at 100% (i.e., maximum quality) and a tiff.
yes, and the bandwidth to send tiffs is far greater. From a Chromira printer, you probably won't see any visible difference in 95% of all files even between a jpeg 9 and jpeg 12 ... only those with real subtle transitions or other types of areas might show a little bit of jpeg artifacts.
As far as sharpness, many labs using printers of this type have default sharpening as part of the workflow, since most of those submitting work have no clue what output sharpening is. You may want to check with the lab. As scott mentioned, it usually takes a little more sharpening than inkjet, so it might look a little bit crunchy on the screen at 100%. I always thought NIk had some presets for this but haven't used it for years. This printer is basically the same as a Noritsu, a Lightjet, or a Durst Lambda or Theta.
Some photographers like the prints without the extra sharpening, guess it makes them look a little more like those printed from negatives (which really weren't usually amazingly crisp). There are many big names in landscape still use printers of this type and silver halide printing ... Peter Lik, Rodney Lough, Tom Magelson (although he's started using a lot of canvas) to name a few.
The D3x files should look just fine at those sizes ... Weve printed quite a few from a D3x and Canon 5d Mark2 on our Chromira as well as an Imetto laser based photo printer (chinese copy of a Durst lambda) on metallic paper ... no problem with those sizes. (unless the file wasn't very good).
