Please explain whats the best & why (without going to 9 inch)

I know you can get a zf plated rear diff which andy g reccomends.
There are quaife rear diffs
& there are gripper.

My car will be near if not 500 bhp once set up i want to spend my money wisley as i have wasted alot changing spec so want to be sure its right for the job.

What differences are the above diffs & whats all uprated in them as im sure there is one that not everything is uprated.

p.s sorry if the above sounds daft