I e-mailed them 6/13, but I haven't heard anything back. SSD is scheduled to arrive today. There's a note on the bottom of the OWC page: 2007 & 2006: Mac Pros utilize four PCIe 1.0 slots. By utilizing the Expansion Utility in OS X, you can configure these slots for your needs. Installing Accelsior in Slot 2 can deliver up to 380MB/s data rate performance, but will reduce video graphics card speed. Installing Accelsior in Slot 3 or 4 will deliver 190-200MB/s data rates, but will not affect video graphics card speed. Slot 1 should only be used for video graphics cards. When I pull up the Expansion Slot Utility, I see the video card "Running at maximum speed" in slot-1. x16. The default configuration is 8x for slot-4, and 16x for slot-1. The OWC guidance implies that only slot-2 (@ 8x) can deliver acceptable performance. Does anyone happen to know why this might be the case?