SATA III can give read/write speeds of up to 600MB/s; whereas PCIe, for example the Samsung 970 EVO, has read/write speeds of 3,500/2,500. I'm wondering whether this difference is actually much noticeable in real world use of Kontakt (which I use in Reaper). I have an Apple iMac Core i7 4.2GHz 27-Inch (5K, Mid-2017) It has a 1TB fusion drive. That drive uses HHD on SATA III, of about 1TB, and then something like 32GB of SSD on the PCIe - super fast. That's used for the OS I think, and maybe some commonly used apps. I'm thinking to make the PCIe drive big enough to put all my apps on (only about 40GB at the moment) as well - if so then maybe 250GB. I'm wondering if Reaper, using Kontakt plugins would work noticeably better/faster if I have Reaper and Kontakt on that PCIe drive vs the SATA III SSD. Anyone know? Also would it make a noticeable difference to have my whole instrument library on the PCIe drive? It would need to be rather big if so! Or, is there no difference in real usage (let's say 20 or so instruments) between that and the usual SATA III SSD (like the 860 EVO (read/write 485/454) or Crucial MX500 (read/write 474/417) for example)? If it makes enough difference, I'll consider doing this: Upgrade SATA III to: Crucial MX500 2TB (3D NAND, SATA, 2.5 Inch, Internal SSD) Upgrade the PCIe to: Samsung 970 EVO 250GB M.2-2280 SSD (probably, or maybe 500GB version?) Otherwise I may as well just upgrade the SATA III to SSD and leave the 32GB of original PCIe type, and put the OS on that. Though I'm planning to upgrade the 8GB of RAM up to 40BG (adding 32GB), and I read one place that the 32GB PCIe might give problems, maybe freezing apps, meaning that with more RAM that drive should also be bigger, which would if true make it worth upgrading that size at least a bit (250GB is pretty cheap anyway) - so if anyone knows about that and can clarify, that would be great! Thanks for any help!