Darren,
Mark's answer is right on the money, but you also asked how the length could affect performance. The length of the bar will move what drag racers call Instant Center (we used to call it Quick Center in the old days). Simple explanation is: By varying the length AND angle of the bar(s) you can adjust the "balance point" of the body weight in relation to the axle centerline. The point of it all is get proper weight transfer for better traction. Making those changes doesn't do much for "rideablity" on the street though.
Verne