For our manual overclocking tests, we used MSI Afterburner. Our best results are as below.
Palit doesn't allow an increase to the power limit when overclocking – which seems sensible considering we were already at 620W at stock! – but we still managed to add 2000MHz to the memory and 240MHz to the GPU, bringing real-world speeds to around 3000MHz.
That overclock didn't net us huge gains – unlike the RTX 5080 and 5070 Ti, the 5090 seems a lot more power limited, so without any increase to power, we only get an extra 1-4FPS in my testing.
Actual power draw is also basically unchanged, considering we did not adjust the power limit slider.