I could't get all your links to work, so you need to check them. If you are planning on using a 550 watt power supply with that video card that is listed, you are in for some heartaches. You need to prepare for the future and I suggest that you start looking for a quality 750 watt power supply to allow some head room. Even with the single EVGA 9800 GX2 you have listed, I would not try that baby without a minimum of a 650 watt power supply by a major manufacturer. Here are some great power supplies you need to consider and think big so you don't box yourself in with a bare minimum power supply:
Seasonic - any model
Corsair - any model
Thermaltake - "Toughpower" series only
Coolermaster - "Real Power Pro" series only
PC Power & Cooling - any model
Silverstone - any model
Seasonic - any model
Corsair - any model
Thermaltake - "Toughpower" series only
Coolermaster - "Real Power Pro" series only
PC Power & Cooling - any model
Silverstone - any model