High-End DDR2 is extremely hard to make
 

IF YOU WANT TO build a high-end gaming machine relying either on Socket AM2 or Socket 775 processors and want to arm these with 800MHz memory, you'll be in an difficult position if you do not want to pay a price premium for top modules.

The problem with DDR2 right now is the number of modules which work at 800MHz - most of the memory chips work at 667MHz, and it is not unusual that even high-end systems ship with slower memory clock.