This is another crucial factor. I sell everything up to 20x30. And when I submit I don't know if my photo will end up in a sidebar in a magazine, or hanging on a 30ft banner in the gym. You have to assume worst case, and simply shoot the best quality you can. But sometimes, the best you can, is just not good enough.
>For other subjects, ISO 1250 is just fine, and the noise is >easily handled in post processing. I've shot entire indoor >events at ISO 3200 and gotten acceptable results printing to >8x10.