Quote - Which of the texture sizes I use depends of course on the scene. A background figure needs no more than 1024x1024, while foreground figures need 2048x2048 or even 4096x4096 (portraits!).

Agreed, and this is also people should always include the largest textures they can in their product. If the texture is too large, it can always be resized down by the user, like in the case of a 4k eye texture. But what if the person using your work needs to do a closeup of an eye and you only have a 128 x 128 texture on it ? It's not like they can enlarge it to 4k and still have the same amount of quality.

And 60% is really too low a quality setting for JPG. At anything below 75-80, you start getting these nasty halos and nickeling around high contrast areas. They don't show up in poser that much since poser blurs textures to hell anyway but in other apps they stand out like a sore thumb.