Difference in gear oil

[Ca_Silvia]

I have seen syn 75-90 and syn 80(?)-140 what is the difference? and what is the best for driving year round?

also if our diffs require gl-4 or something, what if its gl-5 will that work too?

thanks

[teddy]

75-90 will be good for driving year round. GL-4 in the transmission, GL-5 in the open diff.