Disregard the Center Mount and Classic Mount lines for a moment...

The factory line (aka standard line) is -2.5cm back from true center. Measure the ski tip to tail, and divide by 2 to find true cord center. Then move -2.5cm toward the tail. This is the "factory Line."

So, I've mounted my BC's -2.5cm from factory, or -5cm from true center (same location). Unless you land switch a lot, you will probably want to mount in about the same location as I did for a powder ski.

Hi ski neighbor- I'm in North Idaho. I ski ID, WA, MT, WY, BC, so I know your home conditions well. The Mantra is my go-to ski...

I'd recommend the 170 Mantra for you. The Aura and Mantra are extremely similar. However, The 170 Mantra gives you +2mm in the waist, and +3mm in the tip over the 170 Aura, and has a -2m shorter turning radius (18.2m) to boot! Being that you're an aggressive skier and and ex-comp gal, it should be a great fit for you.

The Mantra skis stiff and fast (Volkl's race pedigree), is very stable at high speeds, and holds an incredible edge- characteristics you are probably well accustomed to and like. However, it's still responsive, nimble, and playful. The Sensorwood core and Titanium reinforcement help the Mantra to blow through heavy crud and tracked up areas (this is key for heavy Kootenay snow IMO). The extra width in the tip and waist over the Aura will give you added float in the deep.

For more, you can read my review below: "The Best Quiver Of One Ski." Hope this helps.

I would lean towards the 177 for you (though you could do either). Here are my thoughts behind the 177 choice:

Since you're an aggressive skier, you should able to ski the ski instead of things being the other way around. The Mantra skis stiff, so just be sure to stay in the driver's seat and charge. The 177 will be give you a bit more stability on the steep lines, and a little more float in the deep. Lastly, if you're a young gun and still growing, the 177 will serve you better in the future.

For more, you can read my review below: "The Best Quiver Of One Ski"

Based on the quick measurements I took on my BC's, the factory line is approximately -2.5cm back from true center...

As you likely know, where to mount depends on how you ski, and how you want the ski to perform for you. If you do a lot of switch landings, jibbing, etc, you may want to mount at true center or the factory line (which is pretty far forward IMO).

Personally, I set my BC's up with Marker Jesters, mounted -2.5cm back from factory. This is supposed to be the best mounting point for Big Mountain. I'm told it helps the ski float even better, makes it ski a little stiffer, and is a bit more stable at higher speeds. These are all characteristics I specifically wanted, and suit my style of skiing. For what it's worth, Chris Benchetler recommends a -2 mount for All Mountain.

Depending on what you are looking for- yes, you may want to look at a ski with a narrower waist. I have to preface my comments by saying I have a pair of BC's but have not skied them yet. However, my buddy- whom I solidly trust, had this to say:

The early rise in the shovel and tail of the Bent Chetler (what Atomic calls Pop Rocker) makes it ski like a shorter ski on hardpack. The flotation and stability benefits of the 183 length come back into play in the steep and deep stuff. The BC's are fairly stiff underfoot, with traditional camber, which gives them fantastic edge hold and liveliness. They reward hard charging, and are surprisingly easy to tip on edge for a 123mm wasited ski. With the exception of the JJ, the BC's have about the shortest turning radius of any ski at this waist size. This is further enhanced by the fact that Atomic poured all their race knowledge into the construction of the ski. Add all that to the BC's very low swing weight, and you end up with an absolutely killer ski, that's incredibly nimble, responsive, and capable of just about anything.

So to get back to your question about the length, I think the BC would suit someone of your size and weight just fine. Personally, I'm a pretty big guy- 6'0", 225#, athletic build (think fullback). I tend to charge hard and ski aggressively. I like a stiffer ski, and have been skiing Volkls for years. I wanted a ski that was a solid two-size jump up in waist size from my Mantras. I was actually looking at comparable Volkls, and my tech buddy sold me on the Bent Chetlers. They are exactly what I was wanting, and I'm sure will not disappoint.