The thing is that there is a real latency raise when the cpu memory controller moves to write to the DRAM and DDR2 dram will not be very beneficial to AMD for the reason of stall awaiting write.
AMD did not move to DDR2 for performance. This was done to placate the DRAM manufacturing companies so that they did not have to continue creating two fabs for DRAM. When DDR is obsolete with regards to new motherboards then there will be singular DDR2 Fabs. Secondly, the decision was to impliment DDR2 to negate Intel using it as a selling point.
Intel's legacy Northbridge memory controller will see a far greater advantage from DDR2, especially when the DDR speeds increase and latency decreases.
Now DDR always has a write latency of 1T and this surely benefits an onchip memory controller. This time is dictated by the JEDEC specification and cannot be changed. For DDR2, this write latency depends on the read latency and equals write latency minus one clock which does not benefit AMD's onchip memory controller as in comparison to 1 clock for DDR this is a lacking feature and is at this time the most basic drawback to DDR2. This is heightened with an AMD processor for which the request control is strapped to the onboard memory controller at such a low speed (in comparison to the read latency of that controller) thus creating a read/write stall.
On the legacy Intel Northbridge this latency is already as the move is from processor to dram with the concurrent latency drop anyway.