Is 850W enough for my build?

[Murdoc419]

So I'm planning a build for my new gaming rig and I'm wondering if 850W is going to be enough to power everything. The components are as follows:

Gigabyte GA-Z68X-UD3H B3
i5 2500k (OCed to about 4.2-4.4)
HIS IceQ Turbo HD 6970 (may add a second one later)
8GB Corsair Vengeance 1600
Seagate Barracuda 7200RPM
Samsung Bluray combo
Cooler Master V6 HSF
2x 200mm fans with LEDs
1x 120mm fan with LED
2 cold cathodes
possibly a fan controller

I used this PSU calculator: http://extreme.outervision.com/psucalculatorlite.jsp

Which gave me a recommended wattage of 711 so I figure 850W will be plenty. However after posting this same question on another forum I had some people tell me that 850W is good and less tell me I would need upwards of 1000W. So now I'm not sure what I really need.

Is 850W enough or do I really need to get something larger?

 

[lehtv]

That PSU calculator estimates how powerful of a unit you need. Not how much power your system will use. So it's recommending at least a 700W unit for you. You shouldn't really trust these calculators though. In terms of components, your setup is pretty typical so you should get a better idea of load power consumption by looking at reviews of 6970 and 6970 crossfire. Then buy a good quality power supply that will stay under 80% of its capacity, preferably around 60-70%, during full system load.

http://www.guru3d.com/article/radeon-6950-6970-review/11

System Wattage with GPU in FULL Stress = 361W
Subjective obtained GPU power consumption = ~ 207 Watts

Radeon HD 6970 - On your average system the card requires you to have a 550 Watt power supply unit.

http://www.anandtech.com/show/4061/amds-radeon-hd-6970-radeon-hd-6950/24
http://www.legitreviews.com/article/1488/18/
--> 600W or less during full load, so a 850W PSU would handle 6970 Crossfire comfortably.

In conclusion:
- 2500K + 6970 at stock or with a mild OC (4.2 is pretty mild) - 550W is enough
- 2500K + 6970 heavily overclocked - 650W is enough
- 2500K + Crossfire 6970 at stock or with a mild OC - 850W is enough, 750W would handle it but less optimal
- 2500K + Crossfire 6970 heavily overclocked - at least 850W, preferably 1000W

 

[Termie]

...

--> 600W or less during full load, so a 850W PSU would handle 6970 Crossfire comfortably.

In conclusion:
- 2500K + 6970 at stock or with a mild OC (4.2 is pretty mild) - 550W is enough
- 2500K + 6970 heavily overclocked - 650W is enough
- 2500K + Crossfire 6970 at stock or with a mild OC - 850W is enough, 750W would handle it but less optimal
- 2500K + Crossfire 6970 heavily overclocked - at least 850W, preferably 1000W

These estimates are spot on. In fact, I wouldn't bother with an 850w PSU unless you might go crossfire down the line. 6970 crossfire is quite compelling, so I could see investing in an 850w PSU even if you're not sure about it right now. Just don't do it because you think you need it now. You don't, plain and simple.

 

[lehtv]

Another thing I should mention. Don't buy a 6970, buy a 6950 2GB and overclock it to 880Mhz. The 10% difference in clock speed is the main thing separating these two GPUs, despite the fact that a 6970 costs $100 more!