I believe that no-one can provide a reliable answer for you.
It's most unlikely that you will be able to control your yeast temperature
to within an envelope of 4 degrees anyway, regardless of the average.
I would judge that if you can keep within 10% of the recommendation you will
be fine & unable to detect any difference.
The problem is of course, you will never have a reference standard anyway,
all other things being equal (more or less) there is sufficient variation
between individual home brews, that you can never be sure exactly what
caused which small detectable variation. Often its just age.
Most important IMHO: use a good beer yeast, I accept the recommendation of
my local brewshop on this.
Pete

"JS" <jcs4@frontiernet.net> wrote in message
news:1114689464.e4f2bdac3a6c3240a9c8b73817fa275b@teranews...[color=blue]
> If I use a yeast rated to be optimally fermented at 68 to 72F, but I
> let it work at average 64 to 65, what effect will this have on the
> flavor profile, as opposed to keeping it at recommended temp?[/color]