Rear differential Options

[Sanosuke]

I figure I know the answer to this question already but I just wanted to know the collective opinion on rear differential.

After reading the gear ratio sticky I feel a compulsive desire to plop a forester rear diff on; 4.44 if I remember. Will it fit? Will a legacy 4.111 fit? What is the difference between WRX and STi rear differentials (same ratio)? What has anyone particularly tried? I am willing to be a test dummy for any suggestions.

I believe all(most) subaru parts are interchangeable like legos but I just want to make sure before I go find some pieces and try and swap them around.

Whats a good rally rear diff ratio?