I run the trany/diff/subframe insert from Whiteline like mentioned before and I love the feeling now, it's not too much NVH for me...
I will say, start with the subframe bushing after your trany insert, he remove a lot of play on the rear.
I will say, after this, if you are really minded, do the diff insert just to complete the setup.
But the subframe insert will do like 80% to make the rear more stiffer and I will give 20% for the diff insert to complete.
You have my subframe insert review here :
http://www.ft86club.com/forums/showthread.php?t=60623
Active more power to the wheels!!!