PSU Wattage same Price

[statik7641]

I'm looking to replace my current PSU(which is having voltage fluctutation issues after 7 years of use) and have settled on 2 possible options.The Corsair RMi750w or the Corsair RMi850w.
These are the only 2 high end options available where I live(even online).No EVGA PSU available(except for 1200W ones) or even the RMi650
The thing is,both of them are basically the same price(about 2% more expensive on the 850w) and I was wondering what would be the downside to getting the 850W.I realize this has been asked a few times on the forums through different ways but couldn't get a clear choice out of it.According to CoolerMaster PSU calculator my system uses 400W at max load and from what I could gather a too high wattage PSU becomes less efficient if the system doesn't use too much.
My main question is will the efficiency loss make it not worth getting the 850(especially when in Idle)
Thanks to anyone who can take the time to give their thoughts

 

[vapour]

Do you have a website for pricing?
can you list your rig specs?

 

[geofelt]

A psu will use only the wattage that is demanded of it, regardless of the max capability.
I would consider the 850w unit.
Most power supplies operate most efficiently in the middle third of their range.
When a psu is loafing, it will be quieter because of less need for fan cooling.

 

[statik7641]

Do you have a website for pricing?
can you list your rig specs?

My rig specs are currently:
Mobo:Asus Z170 Aura
CPU:I-5 6600k(OC)
GPU:GTX1070(OC)
RAM:16GB(2x8GB) DDR4 G-SKILL TridentZ(3200Mhz)
Cooler:Corsair H100iv2
Storage:1x64GB SSD 1x1TB WD Black Drive 1x 3TB WD Blue Drive
PSU:Corsair HX750(Old HX,80 plus silver in need of replacement)
Case:NZXT H440

P.S: Pricing is quite different since I live in Brazil and the prices here are insane,but when I looked on other websites,there was a significant price difference between the 750W and the 850W,I found it at the same price cause the 850w is on sale on a specific site,just don't know if the really low usage when in Idle(lower than 20% with the 850) would be damaging,I mean,according to Corsair's website the 850 fan doesn't even kick in until 340W so even when playing normal games(that aren't drawing almost 100%) the fan wouldn't even turn on

 

[vapour]

Even 550 good quality is good enough for your rig with overclocking.

 

[statik7641]

Even 550 good quality is good enough for your rig with overclocking.

Well yeah,I actually intended to go for a 650W but there are only no-names,the only brand options I have are the 750/850RMi from corsair or 1200W Supernova(much more expensive)

 

[vapour]

I will get this:

https://www.kabum.com.br/produto/91025/fonte-corsair-550w-80-plus-gold-semi-modular-tx550m-cp-9020133/?tag=Corsair%20550

 

[geofelt]

Corsair RMi is tier one on this list.
http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html
Pick 750w or 850w as you like
You only need 850w if you ever contemplate GTX1080ti in sli(which is not recommended)