I took the SSD leap a few weeks ago and am totally impressed by the results! Absolutely no issues with Sonar. I feel like I bought a whole new computer.
I had been frustrated with the fact that the more intense EastWest Hollywood Strings libraries would bog down my system. In spite of my powerful computer, I could not utilize the "Powerful System" folders without glitches. EastWest suggests an SSD for best performance, so I started checking around.
When they first came out, the drives were small and, in my opinion, too expensive. Finally, though, they got bigger and cheaper.
I had my eye on Crucial SSD's, and a pro at ADK (where I got my computer) said that people were having success with them. I learned, as well, that I would get the most bang for my buck if I used the SSD as a sample storage/streaming drive, rather than a boot drive. (Having an SSD as a boot drive would make programs load lightning-fast, but would not solve my sample-streaming problem.)
I browsed the Web and found a brand new Crucial 512GB SSD on eBay for $315. At that price, it turned out to be the package without a cable or desktop computer mounting adapter, but it was all I needed. I already had a cable, and my ADK computer came with a special SSD mount on the back of the motherboard.
As advised by ADK, I copied the entire EastWest Hollywood Strings Platinum library onto the new SSD and left Kontakt, SampleTank, Superior Drummer, etc. libraries on my 1TB 7200rpm SATA hard drive. Both this drive and my new SSD are plugged into the only 2 SATA 3 ports on my motherboard. As I understand it, this arrangement allows maximum performance from both sample drives.
I guess at some point I might spring for a 1TB SSD and put ALL of my samples on it, but my system works so smoothly now that I can't imagine it getting any better.