There's a bit of a competitive race for reaching the highest clock frequency on GPU overclocking, the RX 6900 XTs are suitable GPUs alright. This round a Greek overclocker achieved a clock speed of 3321 MHz.
OGS (Greek overclocker) managed to do that with a PowerColor Red Devil RX 6900 XT Ultimate. Breaching the frequency, both the GPU and the Ryzen 5950X were cooled with sub-zero liquid coolant liquid nitrogen. The speed of the processor actually also was nice, at 5.6 GHz. The combination of the both presented itself in a nice 37618 points in the 3DMark Fire Strike Extreme, which is almost 18% faster than the highest score up to that point with similar hardware.
Radeon RX 6900 XT Ultimate from PowerColor breached the 3.3 GHz OC marker