NVIDIA is expected to bring some healthy performance increases to the table later this year with its Ampere architecture. Rumour has it that the RTX 3090 could offer up to a 50% performance increase over the RTX 2080 Ti and may get close to 10,000 points in 3DMark Time Spy Extreme.
https://www.notebookcheck.net/The-NVIDIA-GeForce-RTX-3090-could-almost-hit-10-000-points-in-3DMark-Time-Spy-Extreme-with-performance-improvements-in-excess-of-50-over-the-RTX-2080-Ti.483654.0.html
FAKE NEWS!
...yet...the 90 series have traditionally been dual cards, in which case a 3090 should be at least slightly over double the performance of 2080, considering the generational improvements and scaling issues.
While there is lack of direct comparison,
Comparison 2080 Ti with 3090 is a not quite to apple to apple.
We need 2080 Ti comparison with 3080 Ti. To see the actual generational difference.