For our manual overclocking tests, we used MSI Afterburner. Our best results are as below.
Nvidia RTX 3080 Ti Founders Edition:
Gigabyte RTX 3080 Ti Gaming OC:
Inno3D RTX 3080 Ti iChill X4:
Palit RTX 3080 Ti GameRock OC:
Three of our cards overclocked to basically the same speeds, with the exception being the Inno3D iChill X4. We were able to add 110MHz to the core, but as the power limit cannot be adjusted above 350W, the GPU was unable to sustain as higher of a clock speed as the other three cards.
That difference is reflected in the benchmarks, as the iChill X4 wasn't able to quite match performance of the other three cards. It still provided a small boost over stock clocks, but nothing major.
Even the likes of the Palit and Gigabyte cards didn't massive increases to frame rates, with anything from 4-9% being observed in our tests. This really is just typical of Ampere, with fairly limited headroom overall.