The desired result is more like this photo.  This is the blurred object above, with the non-blurred (rendered with 3D Blur off) on a layer above it.  Used a lighten layer with bottom layer (the blurred version) at 80% opacity.

• I wonder if there's a better way to do this in Photoshop - combine/blend two photos.

This doesn't really show as much motion as desired.  The effect should make forward motion clear in this still image.