I've a 5,1 Mac Pro (2010, 3.33 12-core) and a big fat AMD Radeon R9 280X in lowest PCIe x16 (don't think anything will fit in the x16 slot above). I'm hoping to put two OWC Accelsior S PCIe SSD Addapter cards (mirrored) in the two free x4 PCIe slots - "Accelsior S is the simple solution to add a high speed SATA 6G drive to PCs or silver Mac Pro towers otherwise restricted to 3G architecture." MacSales Tech checked and confirmed two mirrored Acc/S adapters would work but preferred the x16 slots. I'm asking for help calculating the actual difference (loss, if any) of locating the Acc/S SSD pair on the x4 slots, hoping to understand how much two mirrored Acc/S SSDs might be better than one (WRITE speeds - same, but READ speeds go to x2). the adapter - https://eshop.macsales.com/item/Other World Computing/SSDACL6G.S/ the SSD - https://www.amazon.com/Samsung-2-5-Inch-Internal-MZ-75E500B-AM/dp/B00OBRE5UE Thanks.