I'm 5'8" 155 lbs and went with the 180. I'm an expert 50 yr. old skier from the East Coast. Spend half time here and half time out west. All worries of sizing went out the window the 1st day on corduroy and side trail shallow powder. Compared to my 169 Volkl Karmas these skis are more stable but still turn relatively fast. They did exactly what I wanted them to do. They opened up my turns, increased my speed, and added stability and waaaay more flotation.
Skiing side by side with my expert 60 yr. old friend (5'8", 165 lbs) who chose the 172's I took on more speed and less turns. But make no mistake I can easily turn these Souls. His reasoning in the 172 was he skis slower (he is blind in one eye) and prefers staying in tight turns on the mountain.
Interestingly standing them side by side with my 180's it appears the only real difference is the length of the honeycomb tip. They are 3 1/2" longer. Tails look the same and running edge is only a tad shorter. Also his are 104mm underfoot and mine are 106 underfoot. I agree with reviews where I was advised to get the 180 for more flotation. As soon as I got into 4-6" of powder the tips engage and help get the ski on top of the snow.
Purchased with the Tyrolia Attack 13 this 180 Soul rig is very light so I have no sense they are too long. Don't forget as per my measurements the 180 is actually a 177 and the 172 is actually a 170. According to BlisterGear Review the 188 is a 186.5… I had the shop bevel them from a factory 1/1 to a 1/2… I'm very happy with the grip on corduroy. Can't imagine doing anything to them right now - they're perfect...
Skied a DPS Wailer 112 in a 184cm length last year and it was too much. Couldn't make them work on corduroy or hardback… So these 180 Souls are the bomb for me!