I'm looking to start a build with plans to maybe go 2 way sli down the road, and was hoping you guys might know how big of a psu I would need to overclock this (http://pcpartpicker.com/p/sDQ8NG).Thanks for any input.
a good 650 watt is fine. the 650 G2 would be better. maybe get the M5 motherboard and a better case and cpu cooler.
i was looking at the M5 yesterday but one of the reviews from someone who has it said he was aving issues with it so i skipped it.why do you recommend that one over the M7?
so you can get a better case and cpu cooler for this build.
I've been thinking thinking about adding a water cooler,but the only reason I'd get a different case would be if it wasn't compatible with the parts.
I don't know if I'd trust a 650 watt PSU to get juice to my dual 980s. I think if you run everything at stock frequencies you'd be fine, but I'm pretty sure I've tripped over the power headroom in my rig and I've got a platinum rated 860 watt supply.
For reference, I've got an i5 4690k taking 1.25v core voltage cranked up to 4.6ghz. I've had my 980s both up around 1500Mhz with a substantial video memory OC at a power target of 120% with a .14v overvoltage and I'm pretty sure I was drawing too much current for my Corsair AX860 to keep up with, had a few video driver crashes during benchmarking and whatnot.
So yeah, if you're planning to go hard on the OC, I'd aim a bit higher.
Just as some basic napkin math here, if we're looking at the power draw ofa single gtx 980 when agressively overclocked to the built-in 125% power target limit, it will draw just about 205 watts average, as opposed to the stock power draw of around 165. 2 of these will then, ostensibly, draw about 80 watts more power when thoroughly overclocked.
Then we look at the i7, which while being extremely power efficient still will draw more once overclocked. On average, I'd say if you can get it to 4.8ghz you'll be drawing in the ballpark of 20 more watts at the wall. So estimated grand total for a severe overclock to your system would be right at or over 650 watts, which would saturate your intended power supply and possibly lead to system crashes or over current blow outs on your psu.
Which is, in a mathematical sense, why I would suggest getting a bigger PSU. You generally see higher efficiency the further away you are from your absolute power headroom, although high quality psu will run your system just fin right up to the limit, and sometimes just over it, I'd still feel comfortable with a few hundred more watts of power budget. (which is why I went with an ax860, obv.)
how much does 2 way sli actually improve the graphics\performance?
That can be extremely application dependent, so I'd browse through some benchmark tests on the intarwebs to come to a more comprehensive conclusion, but I can tell you that 4k gaming is a thing with dual 980s, whereas it really isn't with a single one.
(Witcher 3, everything maxed except AA, with hairworks ON at 4k, 50+fps at 4k. Glorious. You'd be struggling to push past 30fps with a single 980 at those settings)