Simple - the longer the lever, the less force required to create the same torque.
With that being said, here is a chart with stiffness comparisons for Porsche bars and the adj Tarett bars - unfortunately haven't seen data on the Eibach bar;
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1999 996 C2 - sold - bought back - sold for more
1997 Spec Boxster BSR #254
1979 911 SC
POC Licensed DE/TT Instructor