The catch is it takes more material instructions to do the texture sample. Not much, but still a notable amount.
So by default (it can be changed) any 4k or 8k textures will be set as a virtual texture on import. For existing textures, it’s just a checkbox in the texture settings that you need to enable (classifies it as a new sampler type so you will need to change your materials a tiny bit, just flipping that option).
Virtual texturing means that you have an (almost) flat memory cost for your screen resolution. It loads only tiny pieces of textures as needed, and since your screen isn’t gaining any new pixels, in a perfectly ideal scene it will never need to load more than your exact screen resolution. Obviously, reality isn’t that convenient, but you get the idea. It’s only loading the pieces it needs, making it significantly more efficient than doing it any other way. It can also potentially (not sure if the current version does or not) even omit loading the backfaces of a mesh’s texture entirely.
So when you say you have a ton of 8k textures… unless you actually -need- that full resolution, that doesn’t actually matter. At a distance (meaning, enough resolution to match the screen pixels), there is no difference between a 1k and 8k texture.