I agree the 256 will go first. The people who are super preorder anxious are not the crowd that is going to pause over the slight increase in cost I bet. Those willing to preorder something so new will be all in.
I think it's fairly obvious that whoever is ordering iPhone X, is fairly anxious in general. What it really comes down to, aside from price point, it's someone's storage needs and how they plan on using your iPhone. If you have somebody that takes a lot of 4K videos, photos And has a plethora of applications, naturally the 256 GB would be the better choice. But someone like myself, I can easily survive on 32 GB or Lower, but that's just because that's all I would require for my usage.