depends on how fast you go on the washboard boards..
i hit some seriously rough section of washboard that was about 1km long (roughly .62 miles) and was at a speed of 40km/h (roughly 25 miles an hour) and it handled fine, there was some vibration but the back end didnt kick around like it did when i took the same stretch in my buddies pick up which had leaf springs in the rear.
not sure if its kdss but it was alot better in the 4runner than in the pickup.