yeah displacement is slow in mental ray, but if you dont have a deadline, why not?

I agree about the distance thing. depends on how close your camera is. i've noticed not many people seem to use displacement on the here, unless its from zbrush. might make a nice change. try something basic. (i was thinking a line, or some other kind of squiggle) and if it doesn't look right you can cross displacement off your list and then try normal map or model it.