As for overclocks push the card until you see artifacts or general unstable gameplay.
Sapphire r9 290 overclock settings.
Overclocking the gpu towards 1100 mhz became unstable a nd the memory.
The sapphire vapor x r9 290x i own seems to have default 31mv gpu core voltage asic rating is 76 9 iirc br br originally the oc settings of 1100mhz 1500mhz were stable at stock voltage then i did see some.
Radeon r9 290 overclocking sapphire radeon r9 290 tri x oc ref.
Radeon r9 290 shipping core clock 699mhz 662mhz shipping boost clock 1000mhz 947mhz shipping memory clock 5 2ghz 5ghz shipping.
This resulted in some absolute benchmark busting memory.
Safe temps for r9 290 was 95c so yours should be very similar.
A quick run down on how to overclock your gpu with msi afterburner and unigen valley.
Radeon r9 290 oc 129 419 290 10 300 btw overclocked our maximum power draw has risen an extra 45 watts towards 300 watt.
These settings may not apply to your gpu or set up but some testing wil.
We overclocked our already overclocked r9 290x past its tri x settings to an insane 6 6ghz memory from 5 2ghz on the reference r9 290x.
On a single.
143mv not final but stable so far.
3dmark 11 extreme settings loop graphical test 1 30mins custom fan settings 60 70 sapphire tri x r9 290 oc intel 3570k 4 5ghz 1 32v asus maximus v gene corsair h100 nzxt phantom 410 intel 320 ssd.
Heaven 4 0 extreme settings loop 30mins 1200 1370 overclock.
Keep it under 80 85 and you are fine.
Power limit 50 max core 61c fan speed 2801 rpm 53 vrm 1 56c.