Alright, so I created a thread not too long ago about this, and I have found some more information on this.
The 2000+ Bonnevilles share the same front springs as the 2000+ Deville'*, as can be seen here:
Which is a good thing, because Eibach makes a set of lowering springs for the 2000+ Deville'*.
Now, the rear suspension. After examining exploded views of the 2000+ Bonne'* and the 2000+ Deville'*, they appear to be identical, BUT the springs are not the same PN. This leaves me to believe that they have two different spring rates, hence the different part number.
Bonne Exploded View
Deville Exploded View
Now, I know a few years ago, GM stopped releasing the spring rate info for who knows what reason. This kinda sucks, but nothing I can do about it. So... the next venture I can do is compare the curb weights of the Bonneville'* against the Deville'*. This can kinda give a general idea as to which had the stiffer spring rate.
Anyone have any other thoughts or input on this. Toasty and I have been discussing back and forth over PM about it, figured there might be other interest or input to be had.