I've been thinking about this. I don't think the test you propose has much to do with the real world. The K is basically like a sheet of plywood and they all will flex a lot. What's missing is the inner fenders and firewall which combined make a large box that resists flex or twist.
What the K really does is prevent paralelograming of the front subframe. Here is where the stock K looks to be much better than most aftermarket units. Look at all the triangulation in the stocker vs aftermarket.
Just my take on it...