I assume if one buys a current iMac with the CTO option for a 3TB drive one gets 128MB PCIe connected flash and a 3TB HDD, correct? But what about the other options, 256, 512 and 1TB flash? is that all PCIe, or a combo of the 128 PCIe and a SATA SSD? Seems unlikely since the totals are off. And when you do a CTO build of flash only, does it just leave a hole where a HDD could go? I realize it's not easy to retrofit, but doable. And BTW, on an iFixit guide I saw mention of a SATA connection to flash memory installed behind the logic board; is the flash even PCIe anymore?