To overclock our RX 6800 XT we used the ASUS Tweak II software since this is an ASUS card, as well as GPU-Z.
Taking this GPU as it is, the GPU clock has a factory overclock of 2360MHz and the memory is at reference 16 Gbps (2000MHz).
We were able to modify both parameters easily and achieved 2725MHz for the GPU clock and 2112MHz for the memory clock. This represents a 15% GPU increase and 5% memory increase, which is certainly more than significant. Its rare to see such a huge modification for a GPU clock boost, an impressive result!