I've seen, as I'm sure you have, some pretty breathtaking HDRI-related shots..
But in my recent investigation into such things, it's shown just how many parameters are involved. So many things that make a difference [headshake]
Consequently, it's difficult to get things looking how I want. Part of that I've now come to appreciate is due to the test data I'm using - it's fairly polar, either very bright or very dark. Not a lot I can do about that now
Anyway, check out my thread in GP&T for some screenshots of what happened when I messed with the RGB->Luminance calculations [smile]