planing to buy this components, but not sure about what Wattage PSU to take , run few watt calculators (and got 550w) but that seems too low, plaining to do OC in future
CPU INTEL S1366 Core i7-920 2.66 GHz
VGA ASUS PCI-E ENGTX275/HTDI/896MD3, 896MB DDR3, 448 bit 2x in SLI
The general rule of thumb is a high quality 500 to 550 watt power supply with sufficient current (amps) on the 12 volt rail(s) can easily power a pc system with any single video card made. A high quality 700 to 750 watt power supply with sufficient current (amps) on the 12 volt rail can power a system with two video cards operating in dual mode.
High quality 750 watt power supplies such as those offered by Corsair, PC Power & Cooling, and Seasonics would be excellent choices. They consistently earn high marks in technical reviews. They are stable, reliable, and come with 5 year warranties.
BTW - The brand new Corsair TX750 has earned an 80+ Silver Certification for energy efficiency.