My honest advise just don't over think it like I did , people treat computer hardware like their favourite football team and defend it to the end and pick holes in the opposite team for no real reason when they are both good products.
If you can get a 6900xt for £1200-1400 but the 3080ti is 1700-1800 get 6900xt all day long, if you can get a 3090 at 1400-1500 get the 3090
I went to amd after only having nvidia gpus and was sceptical for no reason other than reading things people say online honestly no regrets I actually prefer the radeon software to nvidias its much more user friendly for me and the image sharpening tool is amazing
If you can get a 6900xt for £1200-1400 but the 3080ti is 1700-1800 get 6900xt all day long, if you can get a 3090 at 1400-1500 get the 3090
I went to amd after only having nvidia gpus and was sceptical for no reason other than reading things people say online honestly no regrets I actually prefer the radeon software to nvidias its much more user friendly for me and the image sharpening tool is amazing