Differences between applying KMeans over PCA and applying PCA over KMeans
There is a difference. In your first strategy, the projection to the 3-dimensional space does not ensure that the clusters are not overlapping (whereas it does if you perform the projection first).

This is because some clusters are separate, but their separation surface is somehow orthogonal (or close to be) to the PCA.

If you increase the number of PCA, or decrease the number of clusters, the differences between both approaches should probably become negligible.