Something else to consider, but does involve a bit of a risk...Anti-virus software. AV software continuously scanning everything that is ever read from the thing can overwhelm the system too, causing freezes. Saturated scenery (like ORBX, but not specifically their stuff) means more data flow throughout your whole system. One little bottleneck and POOF, here comes a freeze while the system catches up.
I do have my Prepar3D installed on an SSD, including all my ORBX scenery and airports. The SSD is exclusive to flight sim stuff. I also have my AV software set to completely ignore this drive, no scans, no live scans of files at read time, etc.
As others have mentioned, make sure your system is optimized with the previously mentioned guides. Even though I had completed optimizing with these guides, I had periodic freezes for about a second and then scenery would "pop" in...disabled my AV and everything went smooth. Now I have it ignore EVERYTHING under this single SSD.
Of course, there is that risk some sort of malware can get in. I perform manual scans of that drive.
Since it is a dedicated sim cockpit computer, I can keep it fairly isolated.