You should use DDR3 basically only if you move to i7.
Really? Why do you say that? There are plenty of 775 mobos that support DDR3. But triple channel does seem to be the exclusive province of the 1366 mobos.
FYI...
JEDEC specs DDR2 DDR3Rated Speed 400-800 Mbps 800-1600 Mbps
Vdd/Vddq 1.8V +/- 0.1V 1.5V +/- 0.075V
Internal Banks 4 8
Termination Limited All DQ signals
Topology Conventional T Fly-by
Driver Control OCD Calibration Self Calibration with ZQ
Thermal Sensor No Yes (Optional)