I have my rear on FULL stiff and front on HALF stiff. The handling is very predictable and you should not have any problems with over steer unless you driving like a bat out of hell around every corner. I drive very hard thru corners and I have to be going ridiculously fast to lose it.
As far as being "squirrely" on the freeway as L8apex stated...I have no idea where that came from. My car has never been squirrely in any situation no matter how fast I was going. You should be totally fine on freeway with bumps.
The reason I have the back so stiff is because of the FWD bucking under acceleration. The stiff rear keeps the weight from moving so hard to the rear keeping the front flat and the front wheels get more traction. Not alot but way better than before.
