efficiency can be important , but in reality when gaming, the most important thing is that it holds the voltage it says it can with enough leeway on the amperage to run your system reliably. A more efficient power supply might give off a little less heat, but really, does a 78 per cent efficient PSU give up much to an 80 per cent efficient PSU? No, not really.
The actual capacity of a the VS450W is 500Watts. Not that it matters, you're not using even 300 watts.
And really, for the price, it's a great budget choice
http://www.hardwareinsights.com/wp/corsair-vs450-review/