I have 17X7990 in total. The core/memory voltage and frequency vary because every GPU is different. For some GPU, I can run 0.99v, with 950/1000 MHz, temperature is 70C. For others, the temperature is 85C, with 0.95V, 870/900 MHz. It depends on the position of the cards in a PC case.

I use powered PCIE risers in open case, I put extra fans to extract heat out.

The original thermal past is extremely thick. I tried to apply thin layer of thermal paste, the improvement is minimal, just 2-5 degree, as the heat sink cannot touch the GPU evenly, even after I adjusted the force with the 4 screws. That could be the reason why manufacturer apply a thick layer of thermal paste.