well, im riding a 176 and a 180, i'm about 5 10 and 210 pounds. the 176 is my park ski, and thought it wouldve been a great length as long as it had been stiffer. my 180s on the other hand, are my fat skis and are amazing for trees and groomers.
i think a 177 would be pretty good for you, you still dont weigh very much, but you're relatively tall if you're still getting taller, so i think that a stiff 175-180 would be good.