I have replaced the balanced 850 pipes on my Commando and fitted 750-style unbalanced pipes. I do not consider it to be a problem at road speeds, myself.
However, if you want high speed performance from a machine a balancer pipe is a good idea. Balancer pipes on any multi generally help engines run well at higher revs, by allowing them to breath better, giving the exhaust gases room to expand into the extra space they provide. The higher up the balance-system is the better. Without the balance pipe, things can get a little restrictive up there when there's a lot of gas leaving the engine. Some people have tried remedying this by fitting wider bore pipes on unbalanced systems, but this seldom works. The problem is back-flow (a classic problem on racing singles). Back flow is caused when a partial vacuum forms on the inner curve of a wide-bore pipe. Most low-level exhaust systems turn the exhaust gases through almost 180 degrees in the space of less than a foot-distance-traveled. At high revs, exhaust gases are leaving the engine at a very high velocity, and sweep around the outside edge of the pipe. The partial vacuum on the inside edge creates vortices in the gas mixture, which allow gas to flow *back* up the pipe, *into* the combustion chamber. I know of a racing Velo-Venom that had this problem. Performance had plummeted, after fitting a bigbore exhaust. When gas analysis was done, exhaust gases were discovered swirling around inside the *carb*! The problem was remedied by the old motorcar racing trick, of fitting a dam in the inner bend of the exhaust, preventing backflow. I've never heard of anyone using this method on a racing twin with unbalanced pipes, but can't see any reason why it shouldn't be done. I believe there are one or two racing people on the list, who might have something to say.
Hmm, I've just read all that, and realized that it's a lot of gobbledygook. Never mind. What I *meant* to say, is that on a road bike I doubt if balancer pipes are all that significant, in their effect upon performance. Our type of bike isn't generally all that revvy, knohow, so I doubt backflow manifests itself all that often. Balance pipes make fitting more difficult and oft as not leak and rust and rattle anyway. Like the two Carb setup at the inlet end of things, I've dispensed with the balancer on my 850 Mando and can't say's I've noticed any difference.
