I have managed to accumulate about 2.5 TB worth of sample libraries, so keeping those on SSD is not practical. I have a primary drive that is SSD, and 4 additional drives - each of those is a 7,200 RPM standard 2 TB HD.
I have no performance bottlenecks running with the above configuration, and everything is wonderfully stable.
I cannot say the same for when I ran with a much smaller set off samples on 2 500 GB SSD drives I had at one time. I lost one of those drives 6 months into having it, and I returned that one and the other one and picked up the standard 7,200 drives instead, and have never looked back.
The stability/longevity of SSD drives will continue to improve - not sure it is there yet, and since things are running smoothly for me, I will not likely convert this computer's drives back to use more SSD's, though will evaluate the situation when gathering info for next computer build.
I also happen to have 32 GB of memory in both of my desktops, so lots of things get fully loaded into memory anyway. I would additionally suggest looking at using 16 or 32 GB of memory for a computer running Sonar. (Some motherboards let you go up to 64 GB).
Bob Bone