All Micron DDR2 is named D9... but not all D9 is overclockable. D9 just indicates that it's DDR2 from Micron.

Overclockable Microns known so far are those of D9Gxx or D9Dxx.

D9Gxx is square, I mean really square, not rectangle or oval or heck not even round.

D9Dxx are the old ones, they are big rectangular chips which looks like DDR, but they're BGA, not TSOP. They are BIG RECTANGULAR chips, not small rectangular chips, and they're obsolete from the current production line.

Other Micron DDR2 cannot be considered overclockable, they even barely reach DDR2-700 sometimes.