If you put on the H&R and did some testing, before and after, then you would have some good evidence. But I haven't seen that done. The stiffer aftermarket bars that are good for drag racing tend to be too stiff for optimum handling. They will feel good, up to a point, like the car is "riding on rails" because they almost completely stop body lean. But they transfer so much weight from the inside rear wheel that the car can go from understeer to oversteer very quickly, without much warning. Not real safe, but that's the kind of thing that will show up on a slalom test. Maybe the H&R is not that stiff, I haven't seen any specs on it. I know the ATR bar is about six times stiffer than the stock bar, and that seems like a huge jump to me. Using boxed lower control arms and poly bushings also adds to the roll stiffness in the rear, so it's easy to get too much.