The clock speed of the computer is not always the overriding factor in
performance. For example, a hideously-complicated program can takes an
hour to draw a picture, but a better-written program can do it in ten
minutes. Here, it depends on how compact the code is, not the processor
speed.
The clock speeds are identical, but the software burned into ROM is
different, causing the three systems to run at slightly different speeds.
The Macintosh SE is possibly 15 percent faster than the Plus, and the SE/30
is four times faster. In any event, the Classic is faster than the Plus by
a maximum of 25 percent. That assumes that you're doing only those
functions that have been optimized in the Classic. Usually, you'll see a
slight increase in performance, and in some you'll see no difference. It
all depends on what you're doing.
There are hundreds of things that influence performance. At the bit
level, all three machines process a single processor instruction in exactly
the same time. Things like processor caching will decrease the time it
takes for that instruction to be loaded from memory, so performance
increases a little there. Taking from the example above, if a routine is
more compact, then it will do its job in fewer instructions. This means the
system does the function faster. All this goes into determining the
phrase, "...up to 25 percent faster than the Macintosh Plus."