Hi,
We have recently been approved by Koni UK & Holland as a fitting centre for the MINI.
We have done a number of installations involving FSD Dampers and Eibach Springs, all with good results. We have asked Koni to confirm for us their thoughts on the use of Eibach/FSD combination & here is the short of it.
After extensive tests by Koni USA, they have discovered that on some applications the FSD Dampers are not complimented by the Eibach (Pro-Kit) springs. This mainly falls on the larger cars (i.e. Saab 93/95). On the MINI in particular the combination works well, as the spring rates are not too far from standard.
Each FSD damper kit is designed to work around the standard spring set up, which will be the most comfortable. A shorter/higher rate spring can decrease some of the effectiveness of the FSD damper, in the case of the MINI this is not too noticeable.
The main problem you will find is the flex in the cabrio chassis, a lot of movement/flex, reduces the effectiveness of suspension. For best results you need to make the shell as stiff as you can (strut brace, lower braces, boot braces & etc.) and then upgrade the suspension.
Re: Coilovers - by the time you have had a set of FSD dampers and Eibach springs, you are not too far from the cost of a KW V1, which will give you adjustable ride height. I'm not sure how much more beneficial the damping adjustments would be, we find that a lot of customers don't tend to even adjust them after initial installation let alone keep trying different settings. Hence it can be a waste of money to pay for the adjustable damping.
Andrey
PS. If you still running run flats then you need to get rid of them as they do nothing for comfort and handling.