Here is another point. Do you know how stiff the stock bar is? Do you know how stiff any aftermarket bars are? No? I'm not worried about the exact spring rate of the bar when I have nothing to compare it to. I'm worried about if I like how the car feels after when I drive it. I dont care what the bar rate is if I like the way it feels. What I'm making will not be far off whats already on the car and I dont see the huge issue with it. If I'm using a bar thats almost exactly the same size as whats on it now and going from a poly bushing to a bearing what exactly is going to go wrong?

Does that calculator take in to account how much force you loose when you use rubber bushings or when you use polyurethane bushings? no? You're overly complicating things.