It used to be 5.9, but if you look on the performance index page, it clearly says it's a scale between 1 and 7.9. The cumulative score is whatever the lowest rated component is, as also clearly stated, because your system will only be as fast as the slowest link. That's almost always the hard drive. Hard drives have seen the rest of the computing world pass them by, and then lap them a few times for good measure. SATA has done little to close the ever widening performance gap.
Just don't fall into the trap so many do, and start obsessing over the score. A 5.9 rating for a hard drive is about as good as you can get. Far too many people get sucked into the world of benchmarking and then spend their days obsessing over squeezing every last bit of performance out of their system rather than actually USING the system for anything. It's fine if you want to identify components underperforming by a large margin, but if we're only talking a couple of percentage points, it's not worth the bother. In your case, everything seems to be performing just as you'd expect. Leave it at that.
I have run the windows rating in windows 7 it rates my computer as 5.9 what is the best rating you can have?
Processor Intel(R) Core(TM)2 Duo CPU T9600 @ 2.80GHz 6.4 5.9
Determined by lowest subscore
Memory (RAM) 4.00 GB 6.4
Graphics ATI Mobility Radeon HD 4670 6.7
Gaming graphics 2798 MB Total available graphics memory 6.7
Primary hard disk 426GB Free (466GB Total) 5.9