Which DIMMs are you using? And how much do they cost?
my alivenf6g is currently running with just a single 2GB regular DDR2; my intention was to buy at least 1x4 or 2x2GB of those cheap high density rams "AMD only" from China, and use the current regular 2GB for my 775 board.
but it's really hard to find a good reference about those "high density memories" actually working well with my board (or any board to be honest).