400 bucks for 6800? Damn thats cheap, I paid 567 eur for mine 5 months ago.

The 7800XT has AI cores, which are dormant now but might get used for whatever AI-enabled feature AMD develops in the future. For that alone, all else being equal, I would recommend the 7800XT. It also has better RT performance than RDNA2, and is very efficient if undervolted, while also overclocking much better than RDNA2.