The strongest rear end we ever found for racing was the Detroit Locker.
It effectively makes it a locked differential if one of the wheels slips.
Very strong, easy to set up, and uses regular lube.
BUT....this type of diff is very loud...very hard...and can be anoying at low speeds.
When entering a corner at lower speeds...if you down shift while turning...the diff will lock and unlock several times....sort of a clunk/click/clunk/click sound...with a lighter car can even make the car jump a little which would not be good for corner traction.
The only other option I can think of is a spool type.
Bob

Guard, ZF, Quaife, Giken, Kaaz, OBX .. pretty much in that order.

yep. Great in an fj40 but would be a handful in a 911!

Got Detroits in both front and rear of my turbo diesel Landcruiser. Off road, it's otherworldly, on road, it's ill mannered, noisy clunky and almost unbearable. Tall, soft springing, coupled with long travel makes for an interesting road experience.