Iv'e done the crops, and they are interesting. First, close up at 5.8m from a £10 note. I have cropped the left hand side with Britannia and upscaled the 500 1.4x with Gigapixel (500mm x 1.4) and compared with the 100-500+ 1.4xTC (700mm). The analog upscaling with the extender does eke out a little more detail, but loses acutance (edge sharpness), and I am not sure I would recommend it.