I understand the role of viewing distance in relation to print sizes, however the question is how to get a print that looks great at close distances.
So what are the steps to get a fine-art quality 60 inch wide print that stands up to close inspection?
a. Using lower dpi?
b. Up-scaling and then using 300dpi?
c. Output at native 100% size and let the printing-shop take care of the everything?
d. non of the above?
Maybe all of the above options under different circumstances.
First off, the raw dpi is only part of the story. The technical quality of the capture is the most important factor followed by the processing techniques even before you get to sizing for output.
Current printers do a fantastic job of getting great output with a lower DPI so that is a good option. You can see the difference in a 200 dpi compared to a 300 dpi when the prints are right next to each other but I serious doubt if in separate rooms most people would be able to tell the difference. If the source file did not have 300dpi it would be even more difficult to see a difference. Current printers are just that good at upsizing and sharpening for optimal output.
Basically, the more resolution you have the better the print will look at large sizes which includes detail and tonality. If you routinely print over 60" you will be better served with the higher dpi and have more room to crop as well.
I know for myself and most professional print makers I am aware of, they will size the print to the native resolution of the output device so they can control the whole process. If you are using a fine art shop then send it to them in native size and let them do the prep if you are unsure.