The basic issue is that sway bars add to the spring rate unless you are hitting a bump where both wheels hit it at exactly the same time and are defected to the same degree. This added rate ( spring rate + bar rate ) may be more than a particular set of shocks is rated to handle. With stock springs where more stiffness to control body roll in corners is necessary, this added bump stiffness may be a good compromise. With aftermarket, stiffer than stock springs, the issue becomes whether the combination is too stiff in terms of ride quality over bumps for the average street driver. ( For autocross - track use you need it even stiffer and an adjustable bar is the way to go )

One of the reasons I developed our progressive springs, really only copying in concept that Volvo offered through their R sport catalog in the 70's, was so that we could add more sway control with the springs ( using a much higher spring rate for the stiff coils than is possible in single rate sport springs), but do so in a progressive manner to preserve the ride quality ( soft coils the same as the stock spring rate ) over small bumps.

There are different rate ( determined by diameter ) sway bars available, at least one in between the IPD bar for the 122 and the stock bar. IPD has also changed the rate ( diameter ) of their bars over the years, I'm not sure this has happened with the 122/1800 bar, but it has for the 140 bar.

John
V-performance.com