Matt
The springs are Kronos 160lbs+ which have the anodised green cup. That's around 11.5 stone up to their next spring which is a 190lbs+ which is about 13.5 stone and over with anodised purple cups.
I weigh 13 stone of pure(ish) muscle so guessed the stiffer ones might be a bit too stiff and unresponsive. In hindsight maybe I was wrong!
You can get replacements off net if you search for Judy springs. These Kronos ones are from USA and work out around 27 quid posted. The guy who sells em is aware of this site, a top bloke, and will avoid you import tak by way he packages it.
I'm sure someone would buy the medium springs in them if you opted for stiffer ones as I fitted them new so they've only done the miles you have buddy.
Prezza