Sorry i couldn't find this information anywhere. Thanks.
non-sport:
sport:
JCW:

 

From what I've seen in other threads it seems the factory uses a variety of springs, based on what options the car has. So, there could be several spring rates for an MCS non-sport, for example.

 

This info is burried in the TSW R56 lowering spring thread. From what I recall the rates are somewhere around 155F/212R. Robin is right though it varies depending on how your car is optioned but the variation is probably not allot.

 

And remember that's just the spring....you are ON the bumpstop which adds to that and is progressive.

- Andrew

 

The R56 was optioned as
:
Cooper
Cooper S
Cooper S w/sport suspension
JCW, which might just be the Sport Suspension but that adds to the question.