I have had a number of different SSD configurations, in several computers, over the past few years.
When they first came out, I had two 512 GB SSD's in one machine, but six months in one of those bit the dust, and each of them ran around $850 at the time. I took store credit on the failed drive, and sold the other, and went back to 7,200 SATA III internal drives for a while - and also was able to pick up 2 nice HDTV's, from the store credit I had received.
After some time, I invested in a couple of SSD purchases, and began using those as primary drives in all computers I built for myself, as well as those I built for others.
I have been running 3 computers for music computers for myself, with 1 primary computer, having the specs you can see in my signature at the bottom of this post. My 2nd computer also has an SSD as its primary drive, and a couple of 7,200 SATA III internal drives for content/projects and for samples. My 3rd computer is one I use for testing out software updates, for Windows, as well as for application software updates - Komplete 8 Ultimate, Arturia V Collection, Sonar, etc..., prior to applying validated updates onto my primary desktop and my 2nd computer (which is a laptop and used when I go mobile).
I LOVE having SSD drives for primary drives, but continue to use 7,200 rpm SATA III internal drives for any additional drives, due to cost, and because they cause no performance bottlenecks in this configuration. The primary drive (SSD) contains only Windows and all applications, but all user libraries (documents, downloads, pictures, videos, etc., are moved by changing the Location tab in each folder's Properties.so that they all live on a secondary drive that is non-SSD). On THAT secondary drive, I also place Cakewalk Content and Cakewalk Projects, and use per-project audio sub-folders within each project's Project Folder. I use a 3rd drive to hold nothing but sample content, so that projects really quickly load up big chunks of samples into memory when loading a Sonar project, and then they stream data quite nicely from that point.
The additional thing that I believe REALLY helps it all work well is having a BUNCH of memory ni each computer. My primary computer has 32 GB of main memory, and both other computers each have 16 GB of memory in them.
My next build, which will replace my current primary computer, will have 64 GB of memory, a 250 GB SSD as a primary drive, a 2 TB 7,200 RPM SATA III internal drive for Cakewalk Content and Cakewalk Projects, and 2 512 GB SSD drives for splitting sample libraries for performance purposes. Those 2 SSD drives for the sample libraries will mostly be read-only in terms of actual use, since they will mostly be for streaming samples and for nothing else.
This computer will also have 2 external 4 TB USB 3 7,200 RPM SATA 3 drives for backup purposes.
I LOVE the performance of SSD drives, for both a Primary drive, and for sample content drives, but get great bang for the buck with great performance using non=SSD regular 2 TB 7,200 RPM internal SATA III drives for user libraries, Cakewalk Content, and Cakewalk Projects.
Again - the other piece to the above is massive amounts of memory, to keep a lot of sample content in memory, where it is at its speediest for playback.
I hope some of the above info is helpful for you.
Bob Bone