AMD's RDNA2 architecture has been full of surprises, especially in its ability to hit astronomically high core frequencies compared to the Nvidia competition. But, it appears we haven't seen the best of what RDNA 2 can offer. Patrick from Twitter has tweeted that the RX 6900 XT can hit 3 GHz (if cooling isn't a bottleneck) before running into artificial limiters. Similarly, IgorsLAB shared specifications in BIOS for the yet unannounced RX 6700 XT, showcasing its official limit of 2950Mhz on the core clock.
Note that these numbers are highly theoretical and way above what these GPUs do at stock settings. Both the Radeon RX 6800 XT and 6900 XT have rated boost clocks of 2,250 MHz. So, unless you're using liquid nitrogen or other crazy cooling methods, it's unlikely that you would hit or be able to exceed the reported 2.8-GHz limit on the 6800 XT, 3-GHz limit on the 6900 XT and 2.95-GHz limit on the 6700 XT.
It makes sense that the RX 6900 XT would have the highest frequency limit, as it is the highest tiered GPU in AMD's lineup and presumably has the best silicon as well. But what's really interesting is that the RX 6700 XT is alleged to have a maximum clock of 2950 MHz while the the RX 6800 XT maxes out at 2.8 GHz. This indicates that the 6700 XT could be great for overclocking.
IgorsLAB dug into the RX 6700 XT's BIOS a bit more and discovered that the board partner BIOSes (AIB partners unknown) feature much higher power limits and higher core voltage than the reference RX 6800. BIOS 1 (which Igor thinks is for the reference spec) is targeted at around 186W for TGP (total graphics power). For the 2nd BIOS (Igor thinks is for a high trim model) that TGP goes up to 211W. And core voltages for the RX 6700 XT are supposedly higher than the RX 6800, whose reference spec allows just 203W for TGP.
If this is true, and the RX 6700 XT cards ship around these specifications, we could see the highest factory overclocked RDNA2 chips on the market. The 40 CUs on the RX 6700 XT would potentially be fed with more juice, allowing higher frequencies on air, and only having 40 CUs means it's much easier to cool vs. 60 CUs like on the RX 6800.