you should get skis that are a little too big for you, since you are only 11 years old and will grow into them. I ski on the Lib Tech NAS and its a 156cm and its the right size maybe even a little too small for me. But the NAS is light and the magne traction makes it a very very very good all mountain and park ski. I found that the NAS (narrow ass snowboard) is one of the easiest skis to spin with. They are great skis and i havent had a problem with them. Pick them up ASAP from evogear because they are on sale for only 230$. Get them quick, i guaruntee you will be satisfied. Heres the link for evogear....check it out.
http://www.evogear.com/outlet/skis/lib-technologies-park-nas-striped-man-stripes-2007.aspx