I have 2 x R9 270s and 1 x RX 580 4gb but looking into buying another card.
Which cards should I be looking at for lower watts and max hash?
Should I buy another RX 580 as they are around the early £200 or look at the GTX 1070 which are at the higher end on the £300?
Rx 580 is the one of the good mining card. In the RX series itself you can buy the RX 570 or RX 470. These also the good option to use for GPU mining. You will get the decent hash power to start the mining process.
Now many people mining monero and their choice widely as the nividia cards only. For best hash rate you can select the 1070 or 1080 8gb cards.