So I was just playing around with my card today and I planned to undervolt it not by the graph just moving the Power Limit slider to 85% instead of the stock 100%, also did +300 on Core clock to reach 2990mhz(in your case it will vary on how much core clock you need to add to reach the same) and +2850 on memory clock.
I am getting 3% more performance with the "Undervolt" settings with 20% less power consumption(360w to 300w) and lower temps which is quiet significant for me, it is stable I've tested it for hours now in different titles and just wanted to share with you guys maybe it might help someone who's looking for more power efficiency while the 5080 is a very efficient card already.
When compared to the overclocked settings, the undervolt profile is 7% slower and consumes 100w less power which is acceptable to me as I'm never going to notice that 7% performance loss.
My overclocked profile is 10-12% faster than the stock card so that is noticeable in some scenarios but the undervolt profile decreases that margin to only 7% which is negligible