Below are sample crops from an indoor photograph of a book-spine at each of the Pentax X70's ISO settings. A crop from the Fuji Finepix S100FS at the same ISO setting is shown next to each crop from the X70. Images below are all unmodified 100% crops from their respective cameras taken at the highest quality setting. ISO and white-balance were set on camera, everything else was left on automatic. The last few crops are of lower resolution because of camera limits.

These crops help determine which ISO settings can be acceptably used on these cameras. As noise increases, most cameras compensate with noise reduction which introduces softness. The result is that, while you can partly reduce noise at the expense of details, the maximum acceptable print size gets smaller as ISO is increased. The point at which a print become unacceptably noisy is a matter of personal taste.

Pentax Optio X70

Fuji Finepix S100FS