I have used these kites quite a bit on the snow and I thought that I would post the differences to give other riders a better idea of the strengths and weaknesses of each kite. They are very different kites, but since you can use them for the same activity it is worth discussing.
Let's start with the Peak 4 8 and 11M kites. The setup of these kites takes less time than a Soul, the one caveat is that the Peak cannot be setup directly downwind in high wind (you can do that with the Soul). So, it is more difficult to find a crossed line or bridle tangle. It would not be a big deal if the Peak was not sensitive to a crossed line, but I have found that the Peak is very sensitive to a crossed line in strong winds and noticeable even in the lightest wind.
The Peak has more bar pressure than the Soul, but seems to have a little more grunt.
The Peak does not jump or glide nearly as well as the Soul, not surprising since the Soul has a better L/D than the Peak. A 10m Soul glides far better than the 11m Peak. Yes, it is possible to glide with the Peak, but you need a steeper hill to make it happen.
Both kites are quite stable (with the exception of a crossed line on the Peak)
The Peak has a better low-end than the Soul as the Peak is so light that it will fly in very little wind. So, if you are equipped with skis, you may be able to fly the Peak 11 when only other huge kites are in the air (Soul 18/20 or Chrono 18). You have to work the Peak much more than the big kites, but since it will fly in extremely light wind, it is just a matter of having well-waxed skis and looping the kite a lot. Compared to a static pull with the larger kites. That being said, it is much more fun to be flying a 21m Soul in light wind as the 11m Peak needs strong wind or a near cliff to glide in light wind.
The Soul has a much better high-end than the Peak. Yet it is more difficult to self-land than the Peak and in high wind will usually result in a bridle tangle on the downwind side of the kite in a self-landing (above 25 knots).
Jumps on the Soul are lofty with excellent glide. Gliding on the 12 and 10m Soul is easy in moderate to high winds. While you have to be near the top of the wind range or on a steep hill to get the large Peak 4's to glide.
I would put a newbie on a Peak rather than a Soul. The Peak is easier to relaunch and less likely to bowtie than the Soul.
Of course, last but not least the Soul relaunches easily on the water, while the Peak was not designed for water use, so the Soul is a true year-round kite while the Peak can be used on the water, you may get a swim if the kite goes down.