I had a lot of stutter with Ultra textures, especially in cities. I have a GTX 1660 TI which only has 6GB memory. The used memory seemed to be very close to that and I think the stutter was caused by textures being constantly swapped in and out. They probably designed Ultra textures for 8GB cards. With High textures, the memory seems to max out at about 4GB. The textures still look good.
I have the same card. I tried lowering textures to high. Performance improved moderately but at the cost of visuals. High textures look very bland compared to the crisper ultra textures. They just don't cut in. Still waiting to see if they will release a performance patch so that I can reinstall the game as I really liked the story and gameplay.
What resolution are you playing at? I'm at 1080p, I set the preset to Ultra, lowered texture quality to High, then set Anisotropy to Ultra x 16. I typically set Anisotropy to 16 in every game because it makes a big difference to texture sharpness IMHO. Yes, I can tell the difference between Ultra textures and High, especially for closeups of characters in cutscenes and Ultra looks much nicer but I do think High still looks very nice overall.
I doubt they'll optimise any further. I think they're a small studio and optimisation is an expensive activity.