I did an air to air photoshoot for someone last year and he ended up wanting 16x20s of a couple images. I had never printed my photos before, so I wasn't sure how they would turn out. And these weren't the best resolution (fairly large crops about 3000px on the largest side) I resized them in photoshop to approximately 6000x4800 and sent them to adoramapix. I was fairly happy with the results, with the exception of a halo around the plane due to the resizing/sharpening. I spent some time in photoshop eliminating the halo and resent it to Adoramapix. I couldn't be happier with the results. The photos looked great.
I guess this is all just to say, make sure the image is clean when you send it to print as what you see it what you get. If there are any little imperfections, fix them before printing. Secondly, AdoramaPix did a great job, I'd highly recommend printing through them.
Constructive criticism is always appreciated.