Hi,
Ive also been running the spec R gear diff for quite sometime now. Most of the time outdoors in mod ive ran 1000Cst has been really good so far but however at Halifiax thicker 2000/3000 is better.
On high grip carpet (ardent) ive tried lots of oils. On 1000Cst the car was twitchy and over-rotated. 2000Cst felt much better and easier to drive but i ended up on 3000Cst as it made the car feel really planted and had even more drive out of the corners.
Jonathan R