I can confirm that the performance of a site generated with RW8 is better than the exact same site generated with RW7. In the screenshot below the top site was generated with RW7 - the bottom site was the exact same (I opened it the file using RW8 and then published to a slightly different URL).
The tool I use, by the way, is Google’s Lighthouse, which has audits for performance, accessibility, and more. You can find out more here: Overview | Lighthouse | Chrome for Developers
Dave