Also the dynamic range you pick up from a scene is somewhat dependant on the lens you're working with. Some lenses are naturally contrasty, and pretty much tap both ends of the histogram in every shot, and others not so much...
If we're just talking about specular highlights, you can get a lot more than 5%. Once it's blown, it's blown. Whether it's 1/3 stop over or 4 stops over. If that's the only thing in your image that's going, then you can sometimes push several stops without blowing anything else, which is a considerable amount of shadow detail.
Well, sure. If you are taking photos of really reflective surfaced in sunny conditions...
Again, it all just depends. But as a vernal (lol, autocorrect) rule its better to avoid any clipping. But certainly if specular are 5 stops above diffuse, then you'd want to clip specular to maintain diffuse.
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Canon Rebel X with 35-80mm F4 - 5.6; Minolta SRT-101 with Rokkor 50mm f1.4; Mamiya/Sekor 1000 TL with 55mm f1.4 My Flickr