Hi, I was running two R9 280X and they were far more powerful than a RX580. I also spent some time with a 290X, which was great in terms of performance, but I had many random crashes, so went to the RX580 and I was very dissapointed, because the performance was a bit lower than of the 290X. So, in terms of performance it goes like this from what I have testd - from high to low (where I have LuxMark LuxBall benchmark results, I put them in parenthesis):
1) Radeon VEGA 64 (27.776 - 31.408 - depending on the configuration used)
2) 2x Radeon R9 280x (I didn't write it down unfortunatelly, but I remember it was above 20.000 - I would expect 24.000, based on the results of the 7970)
3) Radeon R9 290x (14.326)
4) Radeon RX 580 NITRO+ (13.479 - 13.729 - depending on the configuration used)
5) Radeon HD 7970 (12.888) - This should be similar to a single R9 280x.
So going for the RX 570 will definitely not be an performance upgrade ...