I understand that the Nehalem Gainestown CPUs with W and X TDP rating (X5550, X5560, X5570, W5580, W5590) are designed for 1333 MHz memory speed. The E rated CPUs (E5520, E5530, E5540) are designed for 1066 MHz DDR3 memory. Apple runs all E, X and W rated CPUs in the 2009 Mac Pro with 1066 MHz. I have a MP4,1 Nehalem octad with W5590 CPUs which still runs with the original 6 GB memory in 1066 MHz. I'm thinking about more memory and obviously about getting the higher 1333 MHz frequency that the CPUs are designed for. When I asked an experienced user (Tutor) he told me that this is impossible. Both BTO options of 2,66 and 2,93 GHz CPUs also support the faster memory. So it appears likely that some more tech savvy users have looked into ways to tweak the memory or simply fitted faster memory. So my question is how could a memory speed upgrade possibly be achieved.