A bit late to the party, but I have a near identical setup except for a 2080 Super instead of 2080 Ti with similar radiator config and the same case. Good to hear you figured out the block issue. I ran into that too with my GPU block not making proper contact with the die. My temps are also very similar to yours and nothing is overclocked. I am also rocking a 9900k.
GPU is around 50-55c during gaming and CPU is around 40-50c. I run my fans at very low speeds as well because I don't like noise.
Here is my setup: