Can I ask for best settings for r9 280x - 1200/6700mhz? thanx.
1100/1500 works best on my R9 280x - Gigabyte Windforce 3GB models.
higher memory clock = quickly SLOWER mining, higher core doesn't give any better hashrate, lower clocks are a slower taperoff on hashrate.
Other cards may vary, especially other models or other manufacturer cards.
For the 280x, it has 256 memory bus, so it is better to raise the memory frequency. For the 390, 1250 MHz is fast enough.