@edsnova posted:^^^^^^^^^^^^^^^^^^^^See Above^^^^^^^^^^^^^^See Above^^^^^^^^^^^^^^^^^^^^^
Also not mentioned (except obliquely): A Spyder's torsion arms are noticeably longer than those on a Bug or 356: about 26 inches long instead of 16. I think that makes them less prone—though not immune—to jacking.
That an IRS 356 can out-handle the best swing axle 550 tells you all you need to know about the IRS advantage.
I guess we'll see once the two cars are on the same tires.