Well I got my prints this morning, and I'm amazed with the quality.
I expected the 30"x20" to look pixelated or grainy. WRONG, this print is crystal clear and very sharp

I resized it to 4000 x 2833 pixels for the large print, but still expected quality loss in the printed version. It was printed on FujiFilm Crystal Archive photographic paper (fade resistance rating of 150 years), using a Polielectronica Laserlab printer.
The small format prints are some of the best I've had to date, and the colours are spot on. I used their calibration image before adjusting the images for prints, and what I've got on paper is exactly what I see on screen. Delivery was less than 48 hours, and well packaged.
To sum up, I can't fault the service or quality of the prints. They will be getting all my business from now on