Triumph Repair: more on oils, friction reducer, soft metals

Question
Some of the guys racing in Australia are running 85 / 140 Hypoid oil, stating that the Spitfire diff runs very hot. This is quite different to the geneally recomended 80 / 90 diff oil. Do you think this is a good idea or potentially damaging ?
Also, earlier query on use of GL5 oils which have high sulfur content (possible problems with soft metals in bearings) was not addressed - your thoughts ?

Im in Melbourne Australia - 15 c in winter, 25 c in summer.

cheers,

Martyn

Answer
Martyn,

Using a thicker oil will increase the temps in the diff as the oil itself will add some drag (friction) on the moving components.  I could see using better oil and possibly a friction reducer instead of heavier oil.

As to the GL4 vs GL5 issue, the consensus seems to be to avoid the GL5 oil as it's potentially damaging to the yellow metal components in the diff shim setup.  

I'm racing in North Texas... 0c in winter, 40+ c Summer.