I was running the JConcepts 'Medium' moulded inserts in the back of mine, with 'Firm' in the fronts. I tried a set of the standard foam's in 4wd to see how they compared but they only lasted 3 runs before the insert started to break down and the tyre lost grip despite there being plenty of tread left.
Moulded all the way
3204-1 'Firm' 2wd front
3202-1 'Firm' 4wd front
3206-2 'Medium' rear