Getting ready to change transmission and differential gear oil

[AlligatorBling]

Ok, im planning on changing the transmission and differential gear oil in my car in the few weeks. The owners manual says that the recommended manual transmission oil is API GL-4, the recommended differential gear oil API GL-5 ... I have done a little research on the web, finding fluids that have viscosity's that equate to these codes... Im just curious to know if thats actually the best to run for a performance minded driver... Taking into consideration that the owners manual recommends 5W-30 motor oil, and I like to run 20W-50 ....
.... So... my questions are, whats the best fluids/viscositys to run for the transmission and differential? And also, if anyone knows... how many quarts does each hold? Any help will be greatly appreciated :bow:

[adey]

AFAIK 5spd tranny is 2.4quarts
my diff with Japanese rear cover (and clutch type LSD) holds 1.7 - 1.9 quarts, depending on how thoroughly I drain it, and what angle the car's at.

For tranny I just switched to Pennzoil Synchromesh; supposedly the same stuff that you buy at the GM parts counter... but significantly cheaper. ($5 vs $8 per quart) I don't know if it even has a weight/viscosity rating (don't have bottles on me) but it's been good so far; definitely better shifting than the old Mobil 1 I used.
Diff I'm using Valvoline 85-140 DINO oil, not synthetic... and of course, friction modifier/additive. (mine's from GM parts counter... but supposedly it's made by others, too... just don't know who/where!)

edit: this is all for both daily driving and track days... in Socal weather. YMMV depending on driving habits, climate and fluid change intervals! If you have an open diff I'd just run an 80-90 synthetic diff fluid; you probably wouldn't gain much/anything from running heavier weight oil in that... and, of course, you wouldn't need friction additive either.