2x R9 290 + Corsair CX750 W | Crash! help

[gilad215]

hello guys

recently bought this rig with 2x r9 290 and a corsair cx750w

for the first two weeks it worked great with powertune+20. now it crashes every 10 minutes. i lowered the powertune to +10 and now its stable and the khash still hits 820-830k

is it ok? do we even need the powertune? doesn't it saves money on electricity in lower powertuning? or should i invest in a new psu?

thank you guys.BTC