Replying to 179 or 189 Obsethed

I am pretty set on buying a pair of obsetheds for this coming season and i need a little input on size. I am 6' about 170lbs and my all mountain skis are a 183. I plan on using them mainly as powder skis and tree skiing. However I would like to be able to get some decent hardpack performace out of them. I know they run about 4 cms longer than the posted length but I was hoping for some first hand experience as to which size to get. Thanks for any input!