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I would not advise you try unless everything is running stock settings.
Is your CPU overclocked?
I would advise at least a decent 650-700w PSU.
Running at 4.2.
Well I guess the PSU has lasted a good 7 years
Any suggestions for PSU? Corsair?
Slipperz
As it's 7 years old then i would definitely replace it.
Corsair
Seasonic
Enermax
Silverstone
Or EVGA: http://www.overclockers.co.uk/showproduct.php?prodid=CA-002-EA&groupid=701&catid=123&subcat=2466
What's your budget?
See the 7970 has gone up already
Budget up to £120 ish
Slipperz
What's the rational for replacing it based on it's age?
I would add that OCZ quality is questionable, i would advise against them after owning 2 and experiencing issues with more.