I was wondering why the default doc size is 550 x 400? To the best of my knowledge It's neither golden ratio nor any other common ratios...
Good point. When in development I asked that the size be the last document would open like in AI for example but my request was never implemented.
My way around, I made a template that has the size I want and then load from template instead of the default. You could make several templates with the sizes you need and then choose the template that fits your particular need.
Good point, Joel!