Its not going to cause you to lose torque, thats just silly talk.
It will cause the motor to rev quicker, in both directions. Let off the gas, and it will drop revs quicker. Get on the gas, and it will let the motor rev faster. The more weight in your drivetrain, from the flywheel all the way to the wheels, takes horsepower (and therefore torque) to spin. You drop 4 lbs off your tires, you picked up hp (and tq). Drop a few ounces off your flywheel, you'll gain hp (and tq). Don't forget, hp and torque are directly related, you can't gain hp and lose torque at the same time at the same rpm.
As far as low rpm power, who the hell gives a fuck? Its a banshee, there is no power under 6 grand anyways. And if your spending your time trying to gain low end hp, get a 4 stroke.
That being said, I really have no desire to spend the time or money to have it done. Plus there is a (small) chance it could fail.