Best Way to Upgrade Fusion Drive

Do you have a 2014 or a 2015 iMac?

In either case the speeds of the PCIe SSDs are always going to be faster than SSDs on SATA connectors. However the speed increase between SATA SSDs and PCIe SSDs is nowhere near as noticeable for most workloads compared to the speed difference between an HDD (or Fusion drive) and a SATA SSD. So I would consider both options “acceptable” because they are going to be significantly better than your current setup no matter what you go with.

If you have a 2014, the PCIe SSD is going to be bottlenecked by the connection (PCIe 2.0 x2). Because you only get two channels that will limit the speeds of whatever drive you buy. So if you have a 2014 I’d probably just go with the 2TB SATA SSD and call it a day.

If you have a 2015 it’s a bit tricker of a decision, since it will support PCIe 3.0 x4. That will give you pretty much the best speeds available from whatever drive you buy, so you might want to go with a PCIe SSD. That being said, like I mentioned the speed between the two is probably not going to make a huge difference for most workloads. If you need the storage I would probably still go with the 2TB SSD, since it’d be more convenient. (I also can’t stand spinning hard drives and would be mad when using the 3TB drive you’re leaving in there, but that might just be me). But if you really want every bit of speed you can get, then yes the PCIe SSD will provide more performance for files on that SSD.