Experts examined GTA 5 Enhanced. They think Rockstar did better than The Witcher 3 devs
Digital Foundry published an analysis of GTA 5's Enhanced version. Experts believe that one of the new features may come from GTA 6.

In early March, Grand Theft Auto V Enhanced was released as a major update for Rockstar's hit game, aimed at making the PC version the best edition. However, the launch didn't go well, and players pointed out a multitude of problems. Experts from Digital Foundry have now shared their opinions, expressing their admiration for the advanced improvements in GTA 5.
Announcement of features from GTA 6?
The video focuses on the RTGI (Ray-Tracing Global Illumination) feature, which is one of the most notable improvements in the Enhanced edition. Digital Foundry even speculates that it was transferred to GTA 5 from GTA 6, as it is very well developed and built with great care.
The authors of the material believe that in this respect, the devs did a better job than, for instance, the creators of The Witcher 3, which also received ray tracing in the Next Gen update. RTGI present in GTA 5 Enhanced is supposed to give better effects, as it covers all light sources. Implementing this is challenging and demands a big effort, and it is also expected to be showcased in the GTA 6 trailer, further indicating that this feature originates from the forthcoming title.
Therefore, the Enhanced edition can act as a kind of performance benchmark for GTA 6 on consoles. It turns out that RTGI technology is supposed to be quite well optimized for GPU, but it heavily loads the CPU. For the tests, an AMD Ryzen 3600 processor was used (equivalent to the CPU in the PS5 and XSX/S), and the frames per second dropped to less than 50. This suggests that GTA 6 will aim for 30, not 60 fps.
Ultimately, Digital Foundry rated GTA 5 Enhanced version very positively and had no major comments about it. The only thing the experts noticed was the strange behavior of the shadows at some moments.