I know its not apples to apples (hynix vs micron, and 2050 vs 2040), but you'll see my hashrates are pretty constant between RX470 and RX570.

GPU #0 = MSI RX 470 4G HYNIX     @ 1140/2050
GPU #1 = MSI RX 570 4G MICRON  @ 1140/2040
GPU #2 = MSI RX 570 4G MICRON  @ 1140/2040
GPU #3 = MSI RX 570 4G MICRON  @ 1140/2040

Screen #0
ETH - Total Speed: 29.472 Mh/s, Total Shares: 8, Rejected: 0, Time: 00:09
ETH - Total Speed: 29.483 Mh/s, Total Shares: 8, Rejected: 0, Time: 00:09
Screen #1
ETH - Total Speed: 29.439 Mh/s, Total Shares: 13, Rejected: 0, Time: 00:08
ETH - Total Speed: 29.445 Mh/s, Total Shares: 13, Rejected: 0, Time: 00:09
Screen #2
ETH - Total Speed: 29.439 Mh/s, Total Shares: 7, Rejected: 0, Time: 00:08
ETH - Total Speed: 29.445 Mh/s, Total Shares: 7, Rejected: 0, Time: 00:09
Screen #3
ETH - Total Speed: 29.464 Mh/s, Total Shares: 7, Rejected: 0, Time: 00:08
ETH - Total Speed: 29.463 Mh/s, Total Shares: 7, Rejected: 0, Time: 00:09