Buying a new Soul 7, confused on length. 5'11" 180 lbs., low to mid advanced skier, 62 years old. Would the 172 be a mistake? Or would there be any serious limitations with that length? Or not a major difference?
The 180cm for certain. These do not ski like a 180cm in a flat ski. They have a very light touch, turn on a dime and have the broadest appeal between skill levels of any ski I have ever been on or read about. A 172cm would be for someone who is around 5' and/or weighs in the low 100's lb. I have the 180cm (175lbs/5'9 - decent skills) and find that they ski shorter than any other ski I own, each of which is physically shorter.
You will love this ski in 180cm. Enjoy and good luck.
You may find this thread helpful: http://www.epicski.com/t/120313/2014-rossignol-soul-7-the-spork-of-skis
I'm just about the same (although I'm 1" shorter and won't be 62 until next month) and the 180s should be fine.
Quick turning and non punishing tail makes for fun in the bumps (soft ones anyway) and I'm looking forward to skiing the trees with them when I get to NH next month.
You might want to check the effective length of the 180 vs 172 closely. The 180 appears to only have more tip. The effective edge length, and recommended binding mounting point looks to be the same when compared side by side. You don't gain much going to the 180 over 172. It changes at 188.