How much chassis stiffening needed?

This topic comes up pretty often. Most people forget very quickly when XV Motorsports was alive, 2005-2013, they were and still are the ONLY company to ever have the unibodies tested for stiffness on a surface plate. This was done at Multimatic in Canada. This was and still is unheard of. The bodies were tested as a baseline, then parts were tested and added as necessary to get a stiffness value on par with modern performance cars. At the end of the day, the parts that were developed were for B and E body cars, but the concept is the same. Frame connectors contoured to the floor, inner fender braces, under hood brace and radiator support is what it took. Having built several XV cars in house and afterwards, the parts work. It was proven at the time, torque boxes did not help neither did boxing the radiator support. I should also add, the radiator supports were 2x2 box, .125" and mandrel bent. The inner fender braces were also .125" wall tubing. I don't remember the tubing diameter.