Think of this..... what matters is how much resistance force the wheel sees as it moves up and down. The spring rate is simply that... the spring. If it's located (say) on an A-arm with the lower mounting point near the balljoint....it will make for a "stiffer" suspension than if the lower mounting point was more inboard....where more leverage is imparted on the same spring.
See...?
The point is that a stock wheel rate is nowhere near 400 lb/in. More like 100-120 lb/in.
- Wil
EDIT...see what I say here and the embedded links, even though I ( too!) used the wrong term "spring rate", at the time I wrote it. -->
http://forums.pelicanparts.com/showthread.php?threadid=329018