In case of the X10, those files are not exactly made to be printed at sizes beyond A3, if at all - even at base ISO. The 12MP (L mode) are nowhere near ideal 12MP, there are EXR specific artifacts, no proper RAW converters, a lot depends on the structures of your subject and so on. With 4000*3000 pickles on A0 you'd end up at about 85dpi or 3.5 dots/mm and I'd say 2 feet would be the minimum viewing distance but I spent some time experimenting with those files, used different masking, sharpening and upsizing techniques, did a number of small sample prints until I got what I wanted - huge jpgs and the prints. Anyway, I had lots of fun, a great print service and it's not that expensive.