Good advice, but I'm currently using a 980Ti, which really isn't able to drive my 4K monitor with high quality settings.
I won't buy a 2080Ti until the third party overclocked boards come out (which "may" be available for preorder on Monday). I don't expect any significantly better GPU to be available for at least a year or two. Price doesn't matter that much; I've been saving for this purchase (and I'm really glad I waited and didn't buy a 1080Ti back when the miners caused them to be seriously overpriced).
Truly, I've been waiting to buy this video card since March, which is when NVidia would normally announce a new card. I knew I wouldn't be happy with a 1080Ti for my 8K, since I want the highest possible quality settings.