This post features various images and image sizes including a gallery to test the download size of different setups. The post was created using the latest build of the Gutenberg plugin (as of Tuesday August 7 at 4:58pm PST) which includes the Responsive Images in galleries PR.
Note: All images are originally 1600px wide.Only default sizing and positioning is used to change appearance.
Full size image:
Large size image:
Medium size image: