Right, so my original plan was to keep the model as low poly as possible, so I intended to use the lowest sub division level in zbrush as my base mesh (3k polys). However, after testing it out in maya and looking at the final result I was not happy with the look, it looked like it was very low poly and I felt that it would not be good enough for the film. There were problems around the mouth area with the teeth intersecting the mesh in wrong places, so I decided to make a higher version (14k polys) which was the second division up in zbrush. I tested this out in maya and noticed a big improvement in form and details so this is the version I have gone with for the final. It does a much better job of holding the details as there are more polygons to work with, there was no lag or chugging so everything seems to be good.
I also consulted with Clym about whether this would be ok and if he would face any difficulties but he said it was fine and everythings good to go.