I currently ski a 166cm ski for park. I want a powder/all mountain ski though. I'm 5'8 150, do you think I could ride a 183 cm ski?

with respect, i don't think peter's answer is very accurate. i'm 5'9" and about 145# and i've skied the 189cm 139mm waisted bluehouse maven in a resort and loved it. if you're 5'8" and 150 the bent chetler would probably be really good for you. that's the thing with rocker is that the actual running edge of the ski, contact point to contact point, is much shorter and makes the ski ride like a much shorter ski. so that's kindof the reason i think it's only offered in the 183. rockered skis of this type with camber underfoot and reverse sidecut at the tip and tail allow for a very wide range of skiers

yes, but it depends on the type of ski, fat (powder) skis you wont need the lenght because you are small and light and will get plenty of flotation from the width, but if you go for a thinner more on piste ski then you will need the extra length for flotation in powder. the bugger is that there is really no all mountain ski, just all mountain skiers. if you are a good skier you should be able to ski powder on any ski of any length, but there are powder skis which are just not any fun to ski on piste with. the best compromise i can think of is the Dynastar legend or mythic Ryder, in which 176 cm would be fine for you if you are an expert skier otherwise go a little shorter.