I took two sets of two photos …
The first set – shadow detail
Image 1 was taken at f/4.5 for 1/60 second ISO 1000. Image 2 was taken at f/4.5 for 1/60 second ISO 2500 and -1.40 EC was applied in Lightroom.
The results: There is more detail in the shadows in image 2, although because the ISOs are extremely high there isn’t a big different grain wise.
The second set – grain
Image 3 was taken at f/29 for 1/5 second ISO 6400. Image 4 was taken at f/29 for 1.3 seconds at ISO 6400 and -2.50 EC was applied in Lightroom.
The results: As well as there being more detail in the shadows in image 4, there is a startling amount of grain in image 3 compared to image 4.
These tests seem to show that the ETTR method produces better results, both in resolving detail in the shadows and reducing grain at high ISOs.