Am exploring a MacPro1,1 cpu upgrade to be able to run the current 64-bit OS version. Have graphics via ATI Radeon HD 2600 XT 256 MB. I have been using a software work around to run OS 10.9.5, but this hack does not seem to be available for any later OS versions. What are the options for replacing the dual core Xeon chips? No budget for new hardware. Am hoping cpu refresh will get the job done.