your tonal studies are really improving. I think at this stage you should move onto a more analytical approach to these studies.
Rather than trying to make a photo-real copy, break the subject down.
For example, painting/drawing the subject with only geometric planes.
Or taking a more graphical approach and translate the value differences into flat shapes, i.e. treat the shadows as a solid shapes. Think cell shading and Mike Mignola type artwork.
Also, where's my free kitten?