DDR3 still uses a multiplier of 2x. Not? Not sure about it though. If you look at a videocard with DDR3 memory, the mem speed is ofter expressed in two speeds: a real and an effective; the real being half the speed of the effective. DDR5 uses a multiplier of 4x.
Do you mean quadpumped fsb maybe?
I would get some good DDR2 1066 with OC potential (good brand, large stock heatsinks) and OC it if not fast enough. If you have a larger budget, you could go for DDR2 1000-1200.
I think the difference between DDR3 and DDR2 is just the speed, like the diff between DDR and DDR2.