What are your canvas dimensions? And how do you export?

Hello! We are doing sublimation and our maximum printing size is 40x30cm.

So we have used canvas of 5333 X 4148 pixels so we get 300dpi good quality photos.

The problem is that in the order viewer the canvas is huge and not responsive like when you build the product. 

This does not allow us to export products quickly because we have to scroll all the way to open layers -> remove back layers -> and then exporting bounding box.

Any suggestions on how do you work? What size did you set up your canvas and do you get quality images at export?