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Using premium fuel, and performance

I just read the gasoline FAQ at
http://ram.chem.tulane.edu:8080/f-body/trivia/gasoline.html (mentioned
in a previous digest), where it states that using a higher octane than
what is required by the engine is just throwing money away.  Since I've
been using 91 or 92 octane fuel since I got the car I was quite
interested in that...

However, in my BMW's manual (1995 325is) it states, on page 21:

- ---
Required Fuel Quality:	89 AKI or 95 RON

As these engines are equipped with predetonation (knock) sensors, you
can also use fuels with other octane ratings, such as 98 RON or 91 RON.
The higher rated fuels will produce an increase in performance
accompanied by a reduction in fuel consumption, while use of fuels with
a lower octane rating will have the opposite effect.  The official
figures for performance and fuel economy are based on 95 RON fuel.
- ---

So who is correct?  The dealer also claimed that using better fuel will
improve performance on some (but not all) engines, such as BMW's.

As a sidenote, the "official" performance figure for my car (on the
brochure booklet) isn't all that good; 0-60 mph in 8.9 sec (it's an
automatic, that's why), whereas I've seen results in various magazines
indicating 8.5 sec, and even 8.0 sec.  I've never figured out how there
can really be any significant variance in the 0-60 mph timing of an
automatic, so is it possible that the fuel quality could account for
such a difference?  I wonder if the weight of the driver is counted (and
if so, how much), or if they subtract it and "fix" the results
afterwards.

I've noticed that BMW's performance figures are often quite different
from those tested in magazines.  The official 3 series performance
figures are usually quite conservative; the test results always show the
cars to be faster than the official figures, while for other BMW models,
the opposite is true.  For example, one of the Euro car magazines
recently tested the new 540i (automatic) to have a 0-100kph of something
like 7.5 sec, which is a second more than what is claimed by the
factory.  I've always wondered what accounts for these differences,
particularly with automatics, which removes one variable from the
equation.