How close to my power supplys wattage can I get

[Pwigy4]

This is my PC build on pcpartpicker:
http://pcpartpicker.com/p/bHDbnQ

The power supply calculator on pcpartpicker says I should have a maximum of 255 watts. The two power supplys I am between are

http://pcpartpicker.com/part/corsair-power-supply-cp9020104na

and

http://www.newegg.com/Product/Product.aspx?Item=N82E16817256097&nm_mc=AFC-C8Junction&cm_mmc=AFC-C8Junction-PCPartPicker,%20LLC-_-na-_-na-_-na&cm_sp=&AID=10446076&PID=3938566&SID=

One is a 300 watt and the other a 450 watt. The 300 watt is nearly half the price of the 450 watt. The 450 watt is modular which would be convenient considering my mini itx build however the non modular cables should not be too hard to manage. My biggest concern is that my maximum wattage of 255 is too close to the PSUs max output of 300 watts. Is this at all something I should be concerned about? Could my computer be at risk or is the 45 watt difference plenty?

Thanks

 

[ahnilated]

You never want to get to close to the limit of your PSU's power output. As the power supply ages it will become less efficient and put out less power. I would give at least 30% overhead to the power supply.

 

[Pwigy4]

You never want to get to close to the limit of your PSU's power output. As the power supply ages it will become less efficient and put out less power. I would give at least 30% overhead to the power supply.

So is the max wattage of my system being 255 accurate? and if so is 300 watt good for it? Can you give me some idea of the accuracy of pcpartpickers estimate and the PSU of my two selected that is better?

 

[Rogue Leader]

That amount is light, 300 is really pushing the edge. You Really should go for the 450 to make sure its powered both sufficiently and efficiently.

 

[ahnilated]

I would do the 450 also.

 

[geofelt]

Your graphics card can draw up to 150w(75 from the 6 pin connector, and 75w from the pcie slot)
Your cpu is a 65w part.
The 225w may well be accurate, but I would go with the stronger psu regardless.
It will operate more efficiently and quieter.

On your build, I think 120gb is too small for windows.
Make it 240gb at least.
You will currently find that Samsung evo is better priced.
120gb is $59,
240gb is $85 and 500gb is $150.
Consider using the 500gb drive and omitting the hard drive completely.