Fist time buying PSU

I run 2x 970s

PSUs have maximum efficiency at 40%-60% load. I don't know what your build is like, but 750W is more than enough for a single GPU. This does not mean you should never exceed a 50% load. It's just to show that a bigger PSU than you need will result in slightly less efficiency (and a bigger initial cost) at the cost of not having room for a major expansion, such as a second GPU. If you add another drive, it should be able to handle that. Also PSUs become less efficient as they age. Have you used a PSU calculator?

Yes, your operating costs, and the initial cost. You'll need to read reviews on them to find out their true efficiency.

The build as it is at this moment is somewhere sub 240W (but close to 240W )
GPU gt545 nvidia page says max draw is 105W

i do plan to upgrade the gpu in close future, and i plan to upgrade motherboard and cpu at a later point

if aiming to do 40% of max on the psu the 650 seems close at 260W (please correct me math if i am wrong) while the 750 is at 300W

using http://powersupplycalculator.net/ it gave me 324 W
other calculators i found did not have the gt545 replacing it with gtx900 cards gave higher numbers but still under 400

When looking at cost, i am not very picky as i want something that work and will work with the minimum amount of problems, power draw over time can i live with (or i have to eat the psu together with me words)

looking on buyers reviews i find 4 of 5 stars (or equal 9 of 10 example) as a average for the 750 one

If you look at my build, I screwed up on the PSU. I have way more than I need. In my defense, I was new to building computers, and that model had good reviews. There used to also be only the eXtreme PSU calculator. There are a lot more options now, which is good.

It can be difficult to find thorough reviews on an appropriate wattage PSU. I struggled with this when choosing one. I have room to upgrade and expand, but this thing is nearly five years old. I should be looking to replace it soon. I don't think you should bother buying with upgrading in mind, because it probably won't ever happen, and if it does...you'll have to get a new PSU, but yours might be old by that time anyway, so it's just prolonging the inevitable and eating it up in operation costs. If not, you'll have a spare to test with if something goes wrong. Maybe you're not paying the electrical bill, but it all adds up, and it's good to conserve.

the motherboard cpu, gpu i have at this time are now around 3 years old so upgrades are likely for me.

did some googling for efficient at the 750 one

If i rad this correct (something that can fully happen i do not) the efficiently would be 87.9%+ in me likely scenarios
http://www.jonnyguru.com/modules.php?name=NDReviews&file=print&reid=380

That would most likely be if your computer was idle: at the desktop, not doing anything. What do you spend most of your time doing on your computer, productivity, gaming, something else?

Game, web browsing, word, music, movies. everything pretty much. It is the main computer i use.

buying a psu with a potential upgrade in mind is never a bad thing.
If a psu is slightly overkill, that totaly does not matter.

@Wolfsi
I think you should check out some of these articles. (It's on another forum, not sure what the rules are about that.) They should give you some more insight, particularly the Articles and Mythbusting sections.

Read a little on it. now comparing prices and i end up being 17 usd cheaper to go with a 550W

So the price difference being kinda little in the big picture i end falling back on the 40% of 750W possible being optimal just because i find 18 dollars little (had for some reason a plan to spend more then market price seems to be) so i still think super overkill still may end up as a optimal goal. then i can learn from me stupidity and be smarter on a later point.

as how i understand it would be better with something like a 600W
but again here the price different being so little i feel dragged to go over it :S

Maybe do a calculation with what you plan to upgrade to, see what the consumption is on that?

well how i look over it something like 600 would have 40% at what the today system runs at max. but the price difference being so small up i kinda think but then again it would be a overkill even at 40%

Read the "50% Load Myth" article. Although, I only understood it last time I read it, so it does take some time to sink in.

well thinking on aiming at between 40% and 60%

and a 600W would be 40% having the rest for upgrades

I'll elaborate on that a tiny bit. I've had a 500w Bronze Earthwatts Antec green psu for 5 years, it still works today even though I've replaced it in my Primary PC. I liked the PSU so much that I decided their 380w Bronze Earthwatts PSU would be the only PSU I will be using from now on in low power PCs that need refurbishing from friends and family.

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well those numbers basicly only tell you how efficient the psu is at a certain system loads.

For example, if your system is using 298W, this particular psu will be arround 89.9% efficient,
which means that it will pull arround 332W from the wall.
Thats basicly all it says.