I got a 'orrible feeling your expecting way too much from a "normal" map, while they are good for anyone making a game or animations for a one shot render don't bother ~ bump is fine and a lot easier to mess with in a paint proggy

even if I really wanted to use a normal map in blender I'd bake it in blender ........its a lot easier then you might think (is even a button called bake from multires lol )

there is no "one size fits all" answer, saving a second or so per frame on a 20,000 frame render would be awesome but means nothing on a one off 20 min render NOT trying to put you off cycles (I love it) but have a play with a normal map you like and its bump map I think you wont see much diff a lot of the time

have fun