I run the center one, its night and day even with the stock springs- made my car steer on power almost to the point of oversteering.
rule of thumb is to get the center SD first then try the front- the center unit basically guarantee's an improvement in steering (on and off power). the fronts usually aren't needed after you drive with the center
Benjamin White
R/c Monster Team Driver
Jq the car, LST, Sportweks turmoil pro
Unconventional Techniques, Superior Results