Are differences in lenses only seen at 100%?

In an A4 print from the whole image area for most people - no.

In an A4 from the whole image area side by side comparisons without knowing which lens was used - for many advanced photographers - also no. The reason is 10 MP and more cameras with most lenses at most apertures provide more resolution in and A4 print than the eye can resolve.

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Leonard Shepherd
Many problems turn out to be a lack of intimate knowledge of complex modern camera equipment.