gas/octane & 2.8 v6

[Jerry Pretti <jpretti@mariners.com>]

has anyone tried using nonpremium gas in a 2.8 v6 (e.g., a4) in the u.s.?
the owners manual says something along the lines of 'use premium, but if you
can't find any, regular will work with a slight decrease in performance, but
switch back to premium when you find it'.  

if anyone has tried lower octane, were there any noticeable differences
(especially for long distance, boring, freeway driving)?  

the gas choices available here are (by octane level)

87  ---
89 +$.10/gal
92 +$.20/gal

thanks...