I have a 2015 4/4 and was experiencing the same issues with bottoming out and clatters etc that you describe. I had a chat to Cain at wolf performance who has sorted my car better than I thought possible.
Its now more akin to a posh "Caterham". He upgraded the springs to heavier duty - also changed the re-bound ones to suit. This was complemented by a set of adjustable shocks. Car is transformed and no hint of clatter or banging. Handling is greatly improved.
Whilst he was wielding the spanners he sorted the steering with some new bearings and a few tweaks to the alignment which has truly sorted the steering.
All supplied and fitted for less than the other option and with enough change to add a Panard rod.
Cain isn't a salesman and I'm sure he'd be pleased to discuss what he/you can do a 4/4 that's clattering - I'd strongly suggest you speak to him before you decided on the SSL kit or anything else.
Last edited by andymot; 30/12/18 10:52 AM.