I reckon a 20GB 3080 with exactly the same perf as the 3080 10GB gpu for £200 extra would sell amazinglyNo one with an ounce of sense is considering gaming at 8k.
Also, given the small difference in perf between the 3080 and the 3090 and the huge difference in price. How can you possibly insert a good value card between the 2? A 20GB card is going to be at least several hundred pounds more expensive with at best, a tiny improvement in performance.
That would be the GPU i would buy