Look for yourself:
http://www.analogstereo.com/pdf/om/i...anual_2000.pdf
It says that you should use 87 octane or higher in general but at high altitudes you can use as low as 85.
Here is an excerpt or two:
FUEL RECOMMENDATION:
Unleaded premium gasoline with an octane
rating of at least 91 AKI (Anti-Knock
Index) number (Research octane number
96).
If unleaded premium gasoline is not available,
unleaded regular gasoline with an octane
rating of at least 87 AKI (Research octane
number 91) can be used.
However, for maximum vehicle performance,
the use of unleaded premium
gasoline is recommended.
CAUTION
Using a fuel other than that specified
could adversely affect the emission
control devices and systems, and
could also affect the warranty coverage.
Under no circumstances should a
leaded gasoline be used, since this
will damage the three way catalyst.
Octane rating tips
In most parts of North America, you should
use unleaded gasoline with an octane rating of
at least 87 or 91 AKI (Anti-Knock Index)
number. However, you may use unleaded
gasoline with an octane rating as low as 85
AKI number in these high altitude areas [over
4,000 ft (1,219 m)] such as: Colorado, Montana,
New Mexico, Utah, Wyoming, northeastern
Nevada, southern Idaho, western South
Dakota, western Nebraska, and that part of
Texas which is directly south of New Mexico.
Using unleaded gasoline with an octane
rating lower than stated above can
cause persistent, heavy spark knock.
(Spark knock is a metallic rapping
noise.) If severe, this can lead to engine
damage. If you detect a persistent heavy
spark knock even when using gasoline
of the stated octane rating, or if you hear
steady spark knock while holding a
steady speed on level roads, have your
retailer correct the condition. Failure to
correct the condition is misuse of the vehicle,
for which INFINITI is not responsible.
Incorrect ignition timing will result in knocking,
after-run or overheating. This in turn may
cause excessive fuel consumption or damage
to the engine. If any of the above symptoms
are encountered, have your vehicle checked at
an INFINITI retailer or other competent service
facility.
However, now and then you may notice
light spark knock for a short time while
accelerating or driving up hills. This is
no cause for concern, because you get
the greatest fuel benefit when there is
light spark knock for a short time under
heavy engine load.
That's a not a small difference in MPG. You say you used the 87 octane couple months ago. So that means during the winter :O
Linear Mode
