The only time it needs goodly speed is during the initial load.
(OS) Copying an
existing Library into the EMPTY (of books) Library folder area will save some time and wear and tear (rewriting the metadata.db) since it is a slam dunk rather than an Add
Book Reading is not an issue. It is the same kind of storage as in dedicated readers.
You just want QUALITY. Failures are a real bummer (keep your Library backed up. Flash do fail or get lost)
Have you considered a pocket sized (eg Passport ) HD? PURRRformance
for $60 (and gobs of extra space for your tunes, Audio Books)