I made a summary
The improvemens in % are the relative changes compared to the previous step, so the for the Export Brace: (0.64-0.48)/0.64 = 25%
Test1
Baseline 0.66"
Factory crossmember 0.64" 3%
Export Brace 0.48" 25%
Monte Carlo bar 0.48" 0%
Passenger torque box 0.48" 0%
Subframe connectors 0.48" 0%
Subframe X brace 0.475" 1%
Test2
Baseline 0.67"
Cut shock towers 0.69" -3%
MII cross member 0.63" 9%
Subframe connectors 0.63" 0%
Subframe X brace 0.61" 3%
Test3
Baseline 0.62"
rear mounting point forward 0.52" 16%
front mounting point rearward 0.35" 33%
Test4
Baseline 0.44"
Firewall to subframe braces 0.42" 5%
Weld braces to aprons and
shock tower panels 0.41" 2%
Diagonals ("Export Brace") 0.36" 12%
SFC 0.36" 0%
SFC X brace 0.36" 0%
Jacking rails 0.35" 3%
Rear seat divider 0.31" 11%
Test5
Baseline 0.35"
rear mounting point forward 0.19" 46%
Removed SFC X brace 0.19" 0%
Removed seat divider 0.23" -21%
Removed seat pans 0.23" 0%
Front mounting point forward 0.40" -0.74%
Most effective changes
Export Brace 25%
Diagonals 12%
Rear seat divider 11%
MII cross member 9%
Firewall to subframe braces 5%
Subframe X brace 3%
Factory crossmember 3%
Jacking rails 3%
Weld braces to aprons and
shock tower panels 2%
Monte Carlo bar 0%
Passenger torque box 0%
Subframe connectors 0%
It's interesting to see that the simplest mods seem to have the greatest effect. But, as mentioned before, one should keep in mind that although some mods showed little to no improvement in this particular test, it doesn't necessarily mean that they are therefore worthless.