I added Julia's Xcel file to my blog, added a link to it in my Suspension Specs, and here is a link to it:
1) Cusco rear show up as 1.5 - 2.0x stiffer on EC site; not 3.25?
2) you show classica as 1.6x stiffer than Abarth? they're supposed to be softer?
3) you show Progress rear as 17.5mm solid; EC site lists as 16mm solid?
I made the changes as I thought they should be. I'll fix any that are wrong later.
1) I made my estimate using a calculator available on-line. I had to make assumptions about the wall thickness of the Abarth bar. I also had to assume all bars were the same metal. Hopefully Cusco's new data was sourced from actual testing gear. Also did they compare to the Classica rear bar or the Abarth rear bar - makes quite a difference. I'd go with the 2.0 compared to Abarth and 1.5 compared to Classca and assume that's what they did.
2) The Classica bar is 14mm. The Abarth 13mm. Assume the same wall thickness and knowing the bar and arm lengths are the same, the Classica bar must be stiffer. That's why the OP is wanting to try one.
3)17.5 is a value I found a year ago. I don't recall where from. I'd have to go with current published data. As I said in my original reply, the data is HARD to come by when making a decision on what to buy.
Please note that I did not calculate stiffness comparisons for the larger (stiffer) bars because I already saw the Cusco and Megan bars were in the stiffness range I was looking for. When you get to super stiffness, hitting a pothole on the street leaves that one side of the suspension unable to absorb the shock without transferring the shock also to the other side. Super stiff sways work great on a smooth race track. They are rough as heck on most poorly maintained public roads. Suspension is always a compromise of holding the car up and absorbing the shocks of irregularities in the road surface, and looking for balance. For the street, I wanted to balance comfort with flatter cornering. I'm happy with what I have done. Full details of my build are in my forum signature.
The best data comes from forum members who have actually installed particular sets of bars and their experience on their modded 124s; do they perform as expected for the type of driving they do with their cars?
Unfortunately, with our 124 cars, the front sway bar is a bear to change. Most of us cannot afford the time and/or expense to swap it out just to see what another bar will do.