400watts of a good company will cover it nicely (like the ones said above, they are the cherries on the cake.) Generic PSU's, like the ones found standard in that case, will not last nearly as long. Fluctuate dangerously, and will not give out its rated wattage and AMPS on the lines. When generic PSU's go they are likely to take out your system as well, due to a dangerous voltage spike as they giove out their last breath. They will also fill your room with smoke while your eyes are re-adjusting due to a big flash. Good PSU's usually die a quiet death.
I think it would be better to get the SLI-D for the motherboard, to save some cash, and put it towards a good PSU. There is barely any difference between them. The SLI-DR has 8 sata ports opposed to 4 in the SLI-D, which is more than enough.
Overclocking does not void any warranties. My GPU has written on the front of the box in bold text, "extreme overclocking." My motherboard also has software to overclock in windows.
AMD put a completley unlocked CPU multiplier to give even higher overclocks, when your RAM can't go as high as you wanted. AMD 64 range has a multiplier that can go down so you can get better memory bandwidth when overclocking.
Cisco CCNA, Comptia A+, 1/3 through CCNP