One point that a lot of people are missing here when it comes to recommending a smaller PSU. Everyone keeps saying it's a waste of money to get one if you decide at a later time to add an additional vid card and go SLI/CF, or make some other high draw upgrade that would require replacing that PSU with a higher powered one. That's completely incorrect. Think of it this way, how many threads do you see here on OCN where someone is having a problem that they think is PSU related, but they don't have another PSU to test it with? While that high quality 500watter may not power the system in full triple SLI mode, it would be more than adequate to power up the system with one card to test i he system with. It sure beats going out and buying a new PSU just to do some basic testing with (and no, getting one and then returning it is NOT a viable or ethical option).
Also, after two years when you do decide to upgrade there is a good chance that the new hardware will use LESS power than what you currently have. The idea of future proofing is a myth. Phaedrus's reasoning is if they don't have a definite plan to add the additional upgrades then the chances of them doing so it rather small, otherwise they would have mentioned it in their post. A simple response of a good quality 500 watter (or whatever wattage meets the hardware specs) from the Recommended PSU List would be an excellent choice for your current setup. Then add that if they have a definite plan to upgrade their vid cards, go SLI/CF, etc. then a 650, 750, or whatever might be a good option. To me that is a more responsive reply to their post then just saying get a 750watter just to make sure you have enough. Doing that is as bad as relying on a PSU calculator to determine what they need, especially since most of the people making those recommendations don't have any idea about what they are talking about.