better GPU temperature between 60-70°C, you can put an additional fan to keep the temperature stable, almost all my rigs are AMD cards and used to mine in ETH from one year ago though for now isn't a good condition to start mining.
This series I have:
■ R9 series started from 290, this series has hungry power consumption
■ RX series started from 480, 580
■ Vega
When I use the R9 390, I lower the voltage to around 950 mV and clock to below 900MHz to save energy.