The "is 8GB enough" argument has been done to death, there's even a dedicated thread for it if you want to join in. Regardless of that, the 3070ti is pretty much neck & neck with the 6800 in most games at the moment (some wins, some losses), but utterly destroys it when you take ray tracing and DLSS into account (hell my 3070 laptop was getting 25% higher FPS than my 6800 desktop in CP2077 with identical settings, and DLSS set to "quality"!).
Nvidia is also better for VR (if the OP uses that) and in home streaming (e.g. Nvidia Gamestream, Moonlight, etc.).
Don't get me wrong, the 6800 is a fantastic card and I'm very happy with mine, but I'm not going to try and argue that the equivalent Nvidia card (e.g. the 3070ti) isn't better for a lot of things, especially considering it's also £100+ cheaper