From the above I'm guessing you're a very good skier.
The one thing I dont know is if you're using this solely for out west, or for east/west? If solely out west, I'd pick something that's 100mm - 110mm underfoot for frequent powder and/or lightly tracked >=6" skiing. If you're looking for east/west compromise, I think something ~90mm underfoot is your sweet spot, as it should have enough float to handle western powder (that isnt too crazy), while maintaining a good groomed or "no recent snow" performance.
As examples, my powder skis are 105mm & 110mm underfoot, my daily drivers are 90mm underfoot, and my early season/crappy conditions/Poconos skis are 67mm underfoot, and I am the same height as you and 5 pounds heavier, so pretty close. Since we're similar size and skier style, I imagine 178cmm - 182cm is roughly the right length for you.
As for twin tips, you might want to also consider partial twin-tips rather than full twin tips, unless you ride switch and do park a lot.