When overclocking the Nitro+, our best result came with the power limit slider maximised at +15%. We were able to push the GPU core to 2850MHz, with the memory at 2100MHz.
This resulted in a real-world frequency increase of about 180MHz.
That didn't result in huge gains in our real-world testing, with frame rates increasing between 3-6% in the games we tested.
The upshot is that power draw didn't increase much either, by only 6W up to 228W.