In addition to the what's new link, please refer to this link that highlights additional feature releases: https://www.xara.com/uk/designer-pro/whats-new/older/. Also I'd recommend reviewing the release notes to see many improvements that add up to a lot.

Hopefully, you will find that it is beneficial to upgrade from v8.1.1 to v16.3.

Happy holidays,
Matt
CEO of Xara