As with the rear suspension arms, the windup of the front suspension arm bushings contribute to the total wheel rate (effective spring rate at the wheel location). I have not tested the OE wishbone and OE tension arm to see how much they contribute to the wheel rate, but I have tested the M tension arm. The M wishbone contributes nothing to the wheel rate because both ends have ball joints.
The method of testing is pretty simple. Hold the bushing in a vice and load with barbell weights:
Measure deflection with a caliper:
Plot the results:
Because I am measuring deflection at the ball joint and not the wheel centre, the results need to be adjusted by the motion ratio of the wheel relative to the ball joint (= approx 16/19). Loads decrease by 16/19 and deflections increase by 19/16. The net effect is a wheel rate due to bushing windup of 5 lb/in using the M tension arm. OE arms together are likely to contribute about twice this wheel rate.
CORRECTION: the motion ratio argument is wrong. When the ball joint moves 1" vertically, so does the wheel, so the wheel rate due to bushing windup is actually 7 lb/in, not 5 lb/in.