I have a DH67GD (same as DH67BL + frirewire & display port populated) and my graphics perf. figure with bios132 and 2509 driver are 5.1 (aero) and 5.6 (games).
I suggest you install (or reinstall) the last release (2509) and at some point od the install dialog you check the button to accept to run winsat.
Then you ask windows to evaluate again the perf.
This is with windows 7 x64 SP1 all updates.
This because when I installed the previous (2476) revision I neither check for winsat nor make windows evaluate, and the figures where good (5.2, 5.6).
After reading your post I ran windows evaluate and saw 4.6 instead of 5.2. I suspect that 5.2 was the older figure of revision 2462 or before, installed with winsat checked.
Then (today) I installed 2509 running winsat, and reach 5.1, 5.6.
Processor is core i5 2500.