After reading both about the desktop core i7 and xeon w35xx/e and x55xx.. it appears that Apple made the FATAL mistake of allowing non-xeons to be used in our mac pros.. It is therefore correct to say that if one were to replace the w3520(2.66 xeon) with the core i7-920(desktop equi), then it will work without a hinch.. Then the answer remains: DO WE NEED ECC MEMORY?? DO WE NEED XEONS when in reality we can take out singles and duals from the stock processors up to the max.. for instance.. I ordered my w3580 to replace the w3520 which is the xeon 3.33 that apple uses and charges us a fortune to upgrade to... while the desktop equivalent is core i7-980.. If we replace the ECC memory with non-ecc memory and use desktop processors, then why bother with the xeon??? certainly we'd all like to save money here.