I decided to split the Fusion Drive back into separate 128GB SSD and 3TB HDD drives on my iMac 5K, and I much prefer it to the FD setup. I run the SSD as my Boot Drive and the 3TB HDD for storage. I realize this won't be ideal for everybody, but if your considering doing this, go for it. It is very easy to do. I like having control over what I run off the SSD and what I store on the HDD. The SSD in the iMac 5K is PCIe based and very fast. Blackmagic disk speed tests are coming back around 320MB/s Writes, and 700MB/s Reads. I installed the OS and all programs on the SSD, and only run my iTunes directory from the storage drive(I have about 1TB of movies). Works great for me. Just thought I'd share in case someone out there was on the fence about doing this.