I sure someone will chime in with the exact stiffness increase across the board

however the xk / xkr / xkrs all share different dampers yes and also different coil springs .
floaty - xk
firm - xkr
sporty - xkrs

I've had all 3 coil springs in and out if my xk

 

What does SDD mean, by the way?

 

Symptom Driven Diagnostics, it's the Jaguar Approved computer diagnostics software that all the dealers use exclusively to work on all computer-rich Jaguars and Land Rovers.

 

Thanks. And is it possible to change those settings as well with one of those laptops you connect to the diag plug and that's equipped with software to see the error codes? My brother in law has one of those...

 

To change it through SDD you need one of these approved devices (see attached) and SDD software. For your model, you only need Software version 125. Newer versions exist as newer Jaguar/ Land Rover models become available. nothing you need.
You want a dedicated laptop, preferably with a clean install of Windows 7 OS and nothing else on it. There are many threads on SDD here and in the General Tech section. You also need a dedicated charge on the battery while using it for modifications, but you won't if you're just checking codes.

 

Here is the charging policy

 

Be aware though, many parameters are not modifiable within SDD, and Top Speed is one of them unless you have a Master Login, or something similar. Engineering Mode maybe? I can't remember the terminology.

 

Does it work for you? Did it on MY10 and tested (limit set at 300). Limiter was still at 250 (running up to ~265). I've heard that front collision radar/ACC may cause it (keep a speed limiter). And it makes sense as got an error on ACC after an SDD mode. Mentioning specifically MY10 as it had ACC/front radar as a standard if I'm not mistaken.

Let me know if it works for you and how did you handled ACC.

 

Just watched old episode of top gear were Clarkson goes mental with a red 07 xkr and says towards the end of the episode they had one up to 170mph

 

I haven't found anywhere I can test it yet unfortunately but Cee Jay has a hacked 2010 XKR and he said in another thread that he has got his to around 190 mph.