AMD can't magically double the data rate of their memory controllers. In servers, they can't expect to support anything more than what JEDEC ratifies.
I believe the new socket G3 is due in 2009, which should fit rather well with the 12-core chips, if they ever come to pass.
I'm not sure if the pin count is officially disclosed, and that socket should come with the MBX memory extender, which is kind of like the memory buffer of an FB-DIMM stuck on the motherboard.
The pin count and altered memory support might allow for a fair amount of wiggle room for increasing bandwidth to the socket.
AMD better have something ready with that socket. Beckton's multiple channels of FB-DIMMs are going to slaughter anything kept at the current memory bus widths, both in bandwidth and capacity.
As for clocking at 45nm, I'd hope AMD could manage to get to the same clocks it got to years ago.
Realworldtech's article on the latest process technologies shows some marginal improvements, if we assume AMD doesn't do much worse than what IBM's shown for 45nm.
The gate oxide is slightly thinner than 65nm, but my Google-fu shows that at 1.2nm, it's only getting back to what it had at 90nm.
Without metal gates and high K gate dielectrics, we can expect something better, but it's not going to touch Intel.
IBM's reticence to show all the numbers for 45nm, particularly for PMOS--which Intel has seriously improved--seems to give the impression we shouldn't hope for too much.
I'm not expecting much of a miracle over 90nm clocks, if that is any sort of a guide.
For the Athlon lineage, it so far has appeared to be the case.
Without a more significant redesign that really adjusts the pipeline to the concerns of finer geometries, the old problems aren't likely to go away.