Andrew Buck :
500 Watt PSU, which he has. My build only uses around 600 Watts fully overclocked (4770K @ 4.6 GHz @ 1.46 V (BSODS after 4.2 without insane voltages) and my 2 R9 270x's at 1180/1525 @ 1.206 V along with all of my other components) and less than 500 at full load at my normal setup (signature).
Three things ....
1. You are assuming that a PSU "rated as" (not tested as) is capable of actually safely discharging 500 watts .... that is quite often not the case.
2. As a PSU ages, it loses capacity due to a phenomenon known as "capacitor aging".....with high end components, a PSU might show a 15% drop over it's lifetime ..... a budget level PSU could easily exceed 30%.
Check out this PSU calculator and look in lower right .... the range appropriate from the best PSUs tot he worst is 10-50%.....that means the rated capacity of the unit should be reduced by that amount.
http://extreme.outervision.com/psucalculatorlite.jsp
3. Yes, Guru 3D recommended a 500 watt PSU which has but ya gotta read the last line. ...... they went on to say.....
If you are going to overclock GPU or processor, then we do recommend you purchase something with some more stamina.
Given that ....
1) The system will be overclocked.
2) The PSU is not what one would call a sturdy "enthusiast grade" PSU
3) I am concerned about capacitor aging if not now then as time goes on. .... certainly no Japanese caps in here.
Still, OTOH, the R9 series are just rebadged 7xxx series with an aggressive overclock.... as such, i do not expect the card will be able to remain stable and adequately cool at more than 10 % OC .... if it was a nVidia card rated for a 500 watt PSU, capable of 25% OC's then I'd be more worried. Not saying I wouldn't do it, just that I'd be careful.