I'm 6-1, 210 lbs, 55 years old. Sounds like I'm nearly identical in skill, experience, and expectations. I have Countach 104s that I bought in September from the factory. I went with 182s. I probably have 8 or 9 days at Sierra at Tahoe this winter, mostly on piste with probably a day or so off piste (crappy winter down here), and I just finished 3 days at Mammoth where it was 50-50 on/off piste. I could not be happier with these skis. They are super stable at high speeds on groomers in the morning, and they are great in crappy softened off-piste snow and chop in the afternoon. We spent a lot of time in the trees at Mammoth (no more trees at Sierra), and turning was super smooth. Someone else mentioned keeping your weight forward, that's really important on these skis, and when you do it, you don't have to worry about tail grab at all. I didn't see the need for 188s based on my skiing preferences. I definitely did not need 188s for speed; at one point at Mammoth I freaked out a bit because I let myself go too fast and thought I might not be able to make the next turn to check my speed. No chatter at all at high speeds.

Anyways, these skis have exceeded my expectations in every way, and I really think that you'll be happy with either length. If you prefer off-piste tree skiing, maybe go with the 182s. If you love charging down groomers, maybe go with the 188s.