The proposed sizes are:
small = x-767px
medium = 768-1199
big = 1200-x
Do you have an x size in mind for small? By x I mean a size we can not shrink beyond.
Originally I was thinking we can do small-medium-large designs separately but now I think it makes more sense to design them together. Ideally we want designs to have as much consistency as possible.
As an example apple seems to be 385: