Did both a google search and searched these forums and found no DEFINITIVE answer. What I found was a bunch of posts of people wanting to try this, others saying it either may or may not work, and then never concluding with actual testing. My question is this: would a Harpertown Xeon with a FSB of 1333 mhz work in a 2,1 flashed Mac Pro? Or is the X5365 ceiling the ABSOLUTE limit? Has anyone actually tried and failed, and if so, could you post a link to the results? The reason I am asking is I have access to a 1,1 which I plan on flashing to the 2,1 firmware... and as the Harpertowns in question with the 1333 mhz FSB are SUPER cheap (around $5 each), an experiment (even with the possibility of failure), is fine with me. EDIT: I did find a youtube video where one guy did try to install a X5470 (quad 3.33ghz) in a 1,1 without success. However, this was the E0 stepping (SLBBF), which is known to not work in even the 3,1. Perhaps the C0 stepping (SLA-variant) will fare better?