Only if you are overclocking can you use the 800 Mhz speed.
Your RAM is getting its speed to reduce to compensate for the high voltage (2.1 volts instead of the allowed 1.5 volts) which is why you're seeing 533 Mhz speeds instead of 800 Mhz.
The end user difference between 800 and 533 isn't much at all to the point that outside of synthetic tests you'd never notice the difference.
Only if you are overclocking can you use the 800 Mhz speed.
Your RAM is getting its speed to reduce to compensate for the high voltage (2.1 volts instead of the allowed 1.5 volts) which is why you're seeing 533 Mhz speeds instead of 800 Mhz.
The end user difference between 800 and 533 isn't much at all to the point that outside of synthetic tests you'd never notice the difference.