May I interupt, what Blayd is saying, is that his/her model has only 3,000 poly yet look at the detail, for 50k polys your is extremely poorly distributed, having thousands of polys doesnot automatically make your model more realistic or accurate, it all depends on placement and flow of the geometry. I know Zbrush bumps up this a hell of a lot but you could achieve the same results with probably 1/5 of the polys you have used. Check out the topology thread, there is no point having polys for the sake of it, they should each be placed purposefully.
Don't take this to heart, just a pointer. Happy modelling.
If you believe in telekinesis, raise my right hand.