Here is good review of RX 590, but nothing about hashrate:
https://hexus.net/tech/reviews/graphics/124211-amd-radeon-rx-590/

According to review:
"Though no obvious changes in architecture have occurred since the original Polaris XT (Radeon RX 480)
launch in June 2016, this latest GPU, Radeon RX 590, kicks up the core clock by over 20 percent.

Radeon RX 590, therefore, is an overclocked Radeon RX 580 which is an overclocked Radeon RX 480."