So I've got 3 GPUs running now, one RX580 and two RX570s... specifically:

1x MSI RX580 Armor 8GB
2x MSI RX570 Armor 8GB

I can't get good hashrates out of them for Cryptonight.  I'm at around 1950 h/s combined, so less than 700 per card average.

They're all Hynix memory.  I've bios modded all of them using the UberMix strap:

Good HYNIX ONLY 8gb - models H5GC8H24MJ and H5GQ8H24MJ
777000000000000022AA1C00B56A6D46C0551017BE8E060C006AE6000C081420EA8900AB0300000 01B162C31C0313F17

RX580 bios settings are 1300 core, 2200 mem.
RX570 bios settings are 1150 core, 2150 mem.
All are undervolted -75 mv.

Running the latest Adrenalin drivers.

Using XMR-STAK with Intensity 512, Worksize 4, no CPU affinity.

Rest of my system consists of:
G4400 CPU
4GB DDR4 RAM
120GB SSD
1000W Corsair Gold PSU
Gigabyte GA-H110-D3A MB
Windows 7 Pro 64bit

When I bump up the intensity (which many people have advised to do), I lose 50 to 100 hashes per card. 

One of the 570s is hovering around 600 h/s!  So frustrated!