PSU connundrum

[Nickie66]

hi guys!
after comparing lots of power supply listings i have found 3 that aren't too expensive for my project but then i have choices to make between tier and wattage ...
 

Tier A+ : BitFenix Formula Gold 550W
Tier A : SuperFlower Golden green 650W
Tier B+: Deepcool DQ-ST 750W


the hardware would be :
Xeon X5675@4.4Ghz
Gigabyte EX58 Extreme
a number of hard-drives
whatever okay salvaged GPU i can put in there

the thing i'm trying to build is a NAS + virtualized arcade machine on the top of it but i'm broke so HDDs will be mixed up ...

so could it be worth it on long term to go up a couple tiers or is wattage the best bet you think ?
 

[Oalei]

anything is fine for this kinda system use

[Nickie66]

well it's a 24/7 system whose only purpose is reliability with a dozen of mechanical drives and an old 6 cores xeon so i'm not putting a 300W noname in there