Ok, got it installed. My boot went from 118 seconds to 82 seconds, a 36 second savings.
The dictionary now loads up pretty much instantly, but I didn't get as much of a boost to KO/PI. It's faster, I guess (I didn't run a lot of benchmarks), but it isn't "instant". I guess that has more to do with the processor than the access time.
Still, it moves a bit better, and I plan to enjoy better battery life, at any rate.
Anyone want to buy a slightly used 4 GB Hitachi?