The total PSU Wattage this tool recommends will give a general idea of the range of continuously available power (not peak power) at which you should be looking. But if you are planning to build a high end gaming system, total Amperage available on the +12V rails—and how that capacity is distributed—could be as or more important than total Watts of power.
So once you have established the likely power needs of your system, please make sure that any PSU you buy will provide sufficient Amps of current on the various rails for all of your devices, and that it will have the proven reliability, service and support you deserve.
Great tool here.