i believe that you would use all the spings in the kit, the large, medium, and small spring. the difference in the two kits is the small spring. you use the small spring with the 4k kit, and you dont use it with the 3k kit.
^^^Yes. You will re use your stock (large) idle spring and all the spings in the kit if you want a 4K. if you want a 3K just take out the smallest (center) spring. A couple guys have removed just the middle sized spring too out of a 4K kit and like it a lot better. Will fuel to 3200 which is all you really need for a DD because unless you have the mods to support it, 3200 is about where your power curve falls off. i personally run the 4K kit and like it. real touchy pedal though. have never tried leaving the middle spring out, but a lot of guys have and like it.