Hi Guys I am new to this forum but I have read this X1 thread all the way.....
a few rule of thumbs i have:
for the front diff, the higher the oil, the buggy will hold a tighter line in the turn and will have better mid to exit turning. while a thinner oil up front will give you better initial turn in, it will torque out and start to lose the line halfway through the turn.
for the center diff, a thicker oil will distribute your power more equally between all four wheels, yielding better acceleration through turns. a thinner oil will put more power to your rear wheels, yielding better straight line acceleration.
for the rear diff, thinner oils yield better "pivoting" action, but is more likely to spin out. thicker oil gives better straight line acceleration and truer tracking through the rough stuff.