It looks like SSDs are going to get worse over time, unlike hard drives:
SSDs are seemingly doomed. Why? Because as circuitry of NAND flash-based SSDs shrinks, densities increase. But that also means issues relating to read and write latency and data errors will increase as well.
The group discovered that write speed for pages in a flash block suffered “dramatic and predictable variations” in latency. Even more, the tests showed that as the NAND flash wore out, error rates varied widely between devices. Single-level cell NAND produced the best test results whereas multi-level cell and triple-level cell NAND produced less than spectacular results.
This suggests to me that SSDs are never going to break out of the boot-disk niche for hardware builds. I get equivalent read-speads on my striped hard drives as my boot SSD, for that matter.