More than once, have I seen threads on "What are acceptable oil
temperatures".  

I just found this in the Feb. '97 issue of European car, page 82 - perhaps
it may provide another input.  
================
How hot is too hot?
    Before you worry about an extra oil cooler, make sure that your oil
really is too hot.  In years gone past, 180 degrees was considered the
optimum, 180 to 220 normal 911 [Porsche] operating temperature, and 250
degrees the point at which the oil really was too hot.  Modern engine
designers typically feel that 180 degrees is too cold for pest performance,
and it's certainly too cold for best emissions and fuel mileage.
     Greg Brown of Precision Motorwerks, who handles a serious herd of club
racers for customers, has this to say about Porsche oil cooling; "I like to
think that if you don't have 212 degrees, you don't boil water pressure off.
 If you can control it around 220 degrees.  Some of the coolers we've been
using can keep temps on the track around 210 degrees, a number we're quite
happy with.  
     NASCAR racers currently aim for 220 degrees to 230 degrees, but they're
not air-cooled.  Good synthetic oils - Porsche started approving synthetics
for 911 use around 1980  -  can easily stand 400 degrees without self
destructing, although it's doubtful that a 2.7 911 motor would be happy with
those temps.
     So what's the bottom line?  If you regularly race or autocross or drive
in hot climates, and see temperatures in excess of 250 degrees F, we'd
probably opt for a cooler.  If your car occasionally touches 230-240 degrees
F on the track, we'd be happy with synthetic oil.