AMD to Redesign Memory Controller in Bulldozer Chips

LOL - pretty scanty details there :p.

Anyway, they would have to reduce latency some as Nehalem is faster than P2 (and I presume Xeons similarly faster than Optys). Since Sandy Bridge is something like 2/3rds the L3 latency of Lynnfield according to the AT preview, then to keep pace BD will also need an improvement there.
 
It seems the rumahs have the BD IMC at 1866MHz.

And the worst kept secret on the internets is for each 10% you bump the NB speed latency is reduced 3-4% and bandwidth is increased 3-4% --- with 'enthusiasts' clocking 50%+ from stock 2000MHz.

So that gives a little headroom for a nice bump in performance if they harness what is (for the most part) on the table right now ...