Guys, I need some help over here. Hope that some of you sifus here can help me a bit for me in choosing PSU for my rig. Well, here's my spec:

proc: Intel C2D E8400 3.0ghz
mobo: Gigabyte GA-G31M-S2L
ram: A-Data 2Gb DDR2 800
HDD: Seagate 320gb 7200rpm
GPU: Powercolor HD4870 PCS+
optic drive: LG 22x securdisc DVD-RW

So my options are:
1) Silverstone ST50F 500W or,
2) Gigabyte Superb 550W

So, which one should I choose between those 2? In terms of performance and reliability? I'm inclined more towards Silverstone but hey, maybe u guys got some other opinion? Help me out guys T_T

Thanks for the fast reply. But I need a bit explanation why should I choose silverstone over gigabyte. Would either of this PSU could power up my rig or would it cause my rig to kaput in a short time? Either way, my friend and I are looking for a new PSU himself. So, I'll post his spec for him and I hope u guys can suggest a suitable PSU for his rig too.

proc: AMD X2 4000+ 2.1Ghz cooled with CM Hyper-TX
mobo: ABIT AN52S
ram: A-Data 4Gb DDR2 800
HDD: WD 160Gb 5200/7200rpm
GPU: Powercolor HD4850 Play!
optic drive: LG 20x DVD-RW

Currently he's using Atrix 500T 550W. Should he stick to his old PSU or change to a new one? Suggestion?

Hope u guys can help out >.<

Thanks. But is it necessary to switch to ST56F? I mean, do ST50F not enuf? If he's using HD4850 need to use that ST56F, so I'm using HD4870 also need to pick ST56F? I mean, I think I got only enuf budget for ST50F... Help me out guys, do ST50F enuf for my rig?