"Anything above 32-bit - the advantage lies within printing. Although you won't be able to see the extra colors on your PC, you can have an advantage in printing, as those extra colors can be/will be noticable on a print. (or traditional film, etc.)" Errr, AS, CMYK is a smaller colour space than RGB. Which you certainly know from Photoshop, when that exclamation mark appears in the colour picker. HDRI is 64 bits, methinks.

-- erlik