To start, I would suggest using the search function on this forum. You will find lots of information about the im88 from many different sources. Also, you will need to provide specific information about your skiing in order to get specific feedback, like skiing level, preference, frequency, location, etc.
That said, I am almost exactly your size (6'1" / 180), and own the im88 in 186. I bought the im88 as my 1-ski quiver for my 1st year living in Utah, with plans to supplement with a dedicated powder ski next season. It fit my needs perfectly.
As a former racer my skiing style is aggressive, but not necessarily always just fast. I like to drive the ski hard and prefer a damp ski with less "pop" from each turn. After demoing many skis in the 85 - 90 mm range, I found the im88 to be the best suited for my style. Definitely more stable at speed than the others, especially in crud and chopped up pow.
Initially, I thought the 186 might be somewhat difficult in trees and tight spaces, but found them an ideal size for me. The extra length (compared to the 175) makes them great in powder and crud, and they kill it on the groomers. The only area that I would consider the shorter length to be an advantage is in the bumps ... however, my preference is to stay away from the bumps so not an issue.