So I know I'm running a huge risk at sparking up a "this gear oil/combo is best" war, but here are my observations:
Over the break we changed the rear diff oil and transmission oil on 3 of the 4 family Subaru's (so much for plans, I had hoped to do all 4, but ran out of time).
Here's Daughter 2's car in mid change.
All 3 of the cars had unknown gear oil in them, and while not OVERLY stinky, most of the transmissions were darker than the Subaru stuff, and surprisingly in one car (not the jdm) the gear oil turned purple as soon as it contacted spray nine when cleaning up the drain pan.
Observations.
1) The car pictured above had a small issue down shifting to 4th (crunch) if you did not rev match and/or take your time. After the gear oil change, that problem is gone - I tried it, and my daughter, who daily drives it, confirmed this. (this car has light fly wheel, light pulley, 6 puck clutch, all group N mounts, so any "issue" is magnified 10X).
2) The 2004 wrx (mostly stock) was seemingly shifting and sounding fine prior to the change, BUT after it is noticeably smoother up and down shifting (especially downshifting).
3) And this is the big one: On my JDM leggy gt-b, ever since I got it the LSD has not liked turning on bare pavement, and since I started parking in the parkade at work (like 8 pretty tight 180 degree turns to get down to my parking level) the problem was really bothering me as you could hear the rear end "winding up" and then "releasing" when the tire slipped, you could hear it and feel it anytime you had to make a slow speed tighter turn on pavement.
I changed the rear diff oil once a while ago with some CDN tire synth stuff I had laying around, and it made no change. BUT!, Now after the rear diff oil change to the Subaru stuff the "binding" is gone... & the LSD is still working just fine, it will spin both rears when "requested" or get tail happy when you get on the throttle in the slippery stuff.
I was a bit hesitant to drop 300 or so dollars on a bucket of gear oil, but I'm really, really happy and impressed with the results in all three cars,,, I'll add the results of wifeies LGT when I get that done in a week or so.
Centaur had a sale on the buckets just before Christmas, not sure if its still on.