This is from a shop website in Australia, although he is talking more about carve skis than big mountain/park skis:
What size ski should I buy? We regularly get asked this question by customers not sure what size ski they should purchase. The latest evolution in carve skis allows you to ski skis much shorter than a few years ago. If your a man and purchased carve skis even 3 years ago you probably brought 180/184/188 and ladies often come in with 170/178.
The latest skis are wider with a smaller turn radius and are torsionaly stronger and are designed to be skied much shorter. I am 183cm tall and 75 kilo and ski a 167/168/170 cm ski depending on the brand. This length holds better on ice and hard snow while carving a much tighter pure carved turn. I have tested (along with a bunch of other retailers) the same model ski in 167, 174 and 181 cm and everyone was amazed at the performance advantage the shorter ski had over the longer ski. If I arrived late in the morning and had to ski the 181's I found I had to really concentrate to hold and edge on ice and to do carved turns down the groomed was much more work than the more nimble shorter ski.
For the ladies skis from 146 thru to 160cm.My wife now skis on 153/156cm and finds the same advantages. If your a tall lady then try the 160/163 but this should be the longest you go
Sounds like most people would disagree with this, but if it works, do it. I am about 180cms tall, I have skied a 170 Bandit X for all round everywhere use, because I am slack and it is easy to use. I also used 177 x-screams for a while, the length was good, the skis werent. If I am on my skis all day every day (ie instructing), I dont want some four metre battleships under me, cos I will get knackered. I want something easy to ski. I save the longer skis for playtime, when I can actually go fast, or ski the powder, or go in the park.
I have found chin height is easy, forehead height is faster, more stable, harder to turn and will melt your quads if you are unfit, over head height is just the same but worse, but but better for powder. Some people get off on that stuff, some dont. Just get what works for you.
In tractor pulls, a 'full pull' is the best you can get. Ahh, how sport mirrors life.