You don't really want photos at ISO 409600 per se, though, you just want photos at the lowest ISO that can get you the necessary depth-of-field for your shot (here extended with tilt-shift lens) at whatever shutter speed avoids being too shaky. And then you want as high of a dynamic range of possible, so you can distinguish the brightest brights from the darkest darks in a single shot.

If you can do that already with the sensitivity you've brought, higher ISO doesn't buy you anything...