The X-Clicks are made with a 4th side that adds quite a bit more (I thought they said 20%?) more preload than what's available using the stockers.
You can get them from SLP and ShadeTree as well as Hiperf. Everyone's within a buck or 2. ShadeTree always does the big discount thing at the Novi show.....
Me and my 280lb butt have been using them for the last 3 seasons on various sleds and never sacked a set of springs out yet. What I've found is after riding with all the extra preload available, you often find you don't need it as much as you thought you did? Maybe due to other changes you make afterward. Cheaper to find out this way than buying another set of springs, and as said - it's there when you need it, just a quick adjustment away - when and IF you do need them. I think they're great for that reason.
Alatalo - Your thought regarding the extra preload causing a coil bind on the shims is a good one. Hadn't considered that regarding having both installed. I agree on the sit in point as well, but would add, IMHO, that if the X-Clicks will let you achieve the desired sit in, you'll be ahead in the ride game as compared to running heavier springs. I would encourage heavier damping, as you mention - or more/earlier coupling to control bottoming once proper (1g) sit in has been set up.
Something not mentioned often as well, is the fact preload on the front skid spring has a very definite affect on the height the rear runs at as well. Guys dinking with the extra preload to get rid of the dreaded static "droop" might want to try increasing preload there first, before going to the time and trouble of anything else?