New build: Should I exchange 750W PSU for 650W version?

[Bizcochito]

Hi, I've ordered a new system and now I'm hesistant about my PSU choice because I'm worried that the system won't hit the 50% load for efficiency so I'm thinking about exchanging the PSU as soon as I get it. These are my system specs:

CPU: i7 8700K
CPU Cooler: Noctua NH U14S in push pull configuration
GPU: ASUS GTX 1060 DUAL OC 6GB (from old build)
MB: ASUS Prime Z370-A
RAM: 2x 8GB Corsair Vengeance LPX 3200Mhz CL16
SSD: Samsung EVO 850 500GB for system and games (from old build)
HDD: WB Blue 7200 rpm 1TB for storage
PSU: Corsair RM750i
CASE: Fractal Design Define R5 Blackout edition
Additional case Fans: 3x NOX HFAN Blue LED 12CM (from old build)

More info:

-Pcpartpicker stimates 364W for this build.

-This is a gaming pc (no gaming aesthetics tho) and I'm going to overclock the CPU (as far as the U14S allows me) and the GPU. I will upgrade the GPU for a high end one in a couple of years or when I feel the GTX 1060 should be gone.

- My power outlet output is 230V@50Hz which is important from efficiency point of view (see this chart )

- Both 750i and 650i have almost the same prize in amazon.

Should I bother in exchanging the PSU? I'd like to hear some opinions. Thanks

 

[kanewolf]

Even if you are at 20% load you only loose a couple percent of efficiency. Is your electricity that expensive that a few watts difference is worth the hassle of exchanging parts?

 

[RememberThe5th]

I guess if you overclock i7 8700k on 5GHz and 1060 6GB 400W load, soo i guess 750W would go, but everything depends, can you push it to 5Ghz, will it need more voltage, how will you overclock your GPU.How many usb devices etc etc....

 

[Bizcochito]

Even if you are at 20% load you only loose a couple percent of efficiency. Is your electricity that expensive that a few watts difference is worth the hassle of exchanging parts?

I'm not worried about electricity bill, I'm worried about letting a good quality PSU go to waste with an unreasonable low load. Yeah, I see that at low loads the damn thing keeps pretty good efficiency, are Corsair charts that reliable?

 

[Bizcochito]

I guess if you overclock i7 8700k on 5GHz and 1060 6GB 400W load, soo i guess 750W would go, but everything depends, can you push it to 5Ghz, will it need more voltage, how will you overclock your GPU.How many usb devices etc etc....

Honestly I don't think I will get good temperatures with 5Ghz overclock, I think I will find the sweet spot around 4.7-4.8Ghz but who knows, silicon lottery.
I don't have my max GPU overclock settings here but this is what I used as reference back in the day to create my OC profile.
As for USB devices, I use a regular keyboard, a Logitech G502 gaming mouse and an external WD My Passport 4TB hard drive but this last one is not connected all the time.

 

[photonboy]

Power Usage max is only about 250W or so.

170W torture (no dGPU): http://www.tomshardware.co.uk/intel-coffee-lake-i7-8700k-cpu,review-34037-12.html

GTX1060 worst-case is 80W or so?

Even adding fans, HDD's etc I doubt you'd see 300W in more normal gaming.

You do not need a 750W PSU unless you plan to get a larger graphics card.

What matters most is:
a) quality/reliability
b) fan noise (I have an EVGA with ECO MODE to turn off the fans even, but some PSU's have very quiet fans)
c) PSU power doesn't exceed 70% (ish) though I aim for for fan noise (since many PSU's start ramping up fan at 50% load)

 

[photonboy]

Overclocking:
I think aiming for 4.6GHz on all cores is probably the best goal with the Noctua NH-U14S. (and motherboard fan software for optimal profile).

Voltage increase affects power (and thus temperature) the most. Sometimes you can adjust Turbo etc to maintain all six cores at a specific MULTIPLIER (i.e. x46) with minimal to no voltage changes though I have NOT experimented with Coffee Lake. Just know that SOFTWARE or other BIOS defaults may be overly generous on voltage so you may need to fine-tine to keep temperatures low.

Aim for 80degC max sustained load all cores. (not Prime95 but realistic worst-case like Handbrake 100% CPU usage for 10+ minutes)

 

[Bizcochito]

Power Usage max is only about 250W or so.

170W torture (no dGPU): http://www.tomshardware.co.uk/intel-coffee-lake-i7-8700k-cpu,review-34037-12.html

GTX1060 worst-case is 80W or so?

Even adding fans, HDD's etc I doubt you'd see 300W in more normal gaming.

You do not need a 750W PSU unless you plan to get a larger graphics card.

What matters most is:
a) quality/reliability
b) fan noise (I have an EVGA with ECO MODE to turn off the fans even, but some PSU's have very quiet fans)
c) PSU power doesn't exceed 70% (ish) though I aim for for fan noise (since many PSU's start ramping up fan at 50% load)

Thanks for the answer

I know I don't need a 750W PSU and that's why I've created this thread. The thing is I already have it (I received it soon after I created this thread) and I wanted to know if there were strong reasons to exchange it for the 650W version since price is almost the same and apparently I'm losing just a bit of efficiency % as kanewolf said.

I plan to get a high end graphics card, but not righ now since my GTX 1060 is fairly new, I bought it seven months ago for my old old friend i7 860 which I had to overclock to 3.59Ghz to avoid CPU bottleneck (80% load average while gaming 60ºC with some 68 spikes from nowhere, not that bad).

You say no more than 300W? that's interesting, if that's the case then from this chart you can tell that PSU fan won't spin at all. I can't tell if this is ok or not ...

 

[Bizcochito]

I've compared the RM750i and RM650i efficiency graphs and noticed that the 750W version provides more efficiency for any %load so there's no reason for moving down to 650W version and lower wattage PSUs don't have the Link feature so that's why I kept the 750.

That said, my new system is already running (no OC at the moment) and efficiency is 88% for iddle and 91-92% for gaming sessions.