Here is a selection of miner settings to get the most out of your cards, have a play and see if you can get more. These work well for my cards, they might underperform for yours.
Graft Mining Pool
Monero Mining Pool
Intense Mining Pool
RX580 4GB
xmr-stak - 950h/s-1000h/s
(MSI) R9 270X @ -31mV & 1115MHz core; 1450MHz mem (50°C @ 90% fan speed); XMR-STAK 399H/s, very stable
(MSI) R9 280X @ -12mV & 1162MHz core; 1743MHz mem (47°C @ 85% fan speed); XMR-STAK 528H/s, very stable
Sources:
RX 580 4GB: Snider
R9 270X 2GB (MSI): Wor3d
R9 280X 2GB (MSI): Wor3d