James, the hi-res version of the Rainbow Monti really doesn't look good, although it looks fine when it is displayed in a smaller setting.
Rather than guessing at the resolution, have a specific number in mind. For example, if you know you'll need it in print quality, pick the necessary pixel size. For online viewing, you might as well keep it at 1000 pixels or less, unless you have a specific screen size. For example, the rainbow monti is a very beautiful piece, and my monitor is set to 1280 x 960. When I viewed that 10 meg image at 5000 pixels wide, it didn't look clean and crisp. It really should though, based on the camera being used. Perhaps you cropped it too tightly.
Hope you don't mind the specific feedback.