dougjax

I also have looked for comparisons on ARB's. The Eibach's are 32mm, hollow and adjustable, the whiteline's are 30mm solid. Whiteline says that they should be ~60% stiffer than the stiock 26.7mm bar, (they have a PDF that shows comparisons to stock based on diameter). But I cannot find any data for the stiffness on the Eibachs. Due to this I ordered the whiteline's. Solid seems like a better idea in general IMHO. It would be nice if all manufacturers provided comparisons. But as stated by S2K007, the CR diameter with the data provided should give you a clue. But that doesn't help with other brands. If someone has detailed specs on other brands, please share.
There are a lot of discussions on the web about the beneifits of a stiffer FARB, but you need to be careful about whether it's about an AP1 or AP2. Seems like AP1's like to reomve the rear ARB, but AP2's just like a stiffer FARB. Then there are the reports of Miata rear ARB for AP1 FARB???(something like that anyway) It seems it can get complicated. I THINK the CR version uses different springs, shocks, and ARB's, so it isn't aples to apples unless you do the whole package.
But the consensus for AP2 seems to be stiffen the FARB and oversteer tendencies will be reduced, (with stock staggered setup). But I'm thinking that if you go with a non-staggered wheel/tire setup, you might be negating the benefit of just stiffening the FARB, (you might have to go way overstiff, then look at spring rates etc.). I also saw reports of rear wheel lift with high grip R tires and stiff FARB. Which turned into an alignment, springs, shock, spring rate discussion.
I guess the bottom line is the more you change, the more you have to change. When the discussion goes into center of gravity, roll axis's, moment arms, it gets deep quick!