Even though this doesn't answer exactly - XV did this in 2006 by testing overall unibody rigidity on a surface plate. Once the reinforcements were installed, the unibody stiffness ranked in line with modern performance cars. I think the K isn't too bad for a stamped piece. When bolted to rails that don't move, its a lot better.
Unfortunately all I've seen from that testing was a video where someone talks through those numbers. No datasets, graphs, etc that give some sort of reference to the testing. I'd love to take a look at results.
