Yea, I was mentioning the 157 because that's what I ride in the regular CT.
You should keep in mind that since the CTX is a wide board, it will be more stable than it's CT counterpart in the 154.
You'll be fine on the 155 in other words. It's a true twin so obviously something directional would suit you better in the powder. But the it is rockered so that's definitely going to help. You can also set your bindings back on powder days if necessary.
You certainly could do the 158 so don't get me wrong here. It will be noticeable more stable and damp than the 155. At the same time, it will be less playful and lively.