I doubt either one of them makes their own springs..so their sources may well be the same (say, eibach for example).
re: short springs
Order springs from either of them, and they're going to be 470mm, cuz that's the length of the OEM spring. The stock springs come with a good deal of spacer..close to 4" as I recall, and that also gives you something ridiculous like 25mm of preload.
The first two sets of springs I got from jeremy were 470mm (+/- a couple).
I asked both fredette and wilkey why the OEM springs were so short, and why not use the fork for SPRING as opposed to spacer. Fredette said weight. Wilkey also said weight...hedged a bit and added, 'the kawi engineers must have SOME reason, so we went with the same length.' He also mentioned that motion effects take longer to travel over a longer spring..and delay of sensing of movement isn't a good thing.
The weight idea doesn't hold any water imo. Who worries about the weight a WER adds to their front end? There's enough difference in weight of different tires to make the same difference that any additional spring would add. Who worries about that? Both those examples are unsprung weight, too.
It DOES make sense to use the available length of the piston rod for spring. Isn't that the whole purpose?
I first tried a set of .42s from jeremy. Thought they were too stiff. He substituted a set of .40s. They were ok, but one of them collapsed in a few weeks. My riding buddy had his suspension done by a local tuner that uses XR400 springs (late model) if he needs a .40 set. They are about 530mm in length. I asked jeremy for a set of those, he sent them. They are FAR superior to the .40s that I had. Much more compliant. With the first set of .40s, I could feel every pebble, with the XR springs..much of that went away.
The honda springs are hot wound. Most (all, I think) aftermarket springs are cold wound. The former is a superior spring...period.
MX affiliate? Why bother? Send them to jeremy.
When I first got my suspension back from mx-tech, I was not $700+ impressed. It took me awhile to warm-up to the setup. I had a chance shortly thereafter to ride a stock suspended kdx (same year as mine, same miles etc). Wow. The stock bike scared the pants off me!
I've since grown to appreciate jeremy's suspension work a BUNCH. Yep..a lot of bucks..but also a lot of result. It's great to have riders with decades of experience say, 'Nice suspension' when they ride my bike.
'Yes,' I say. 'It is!'
If you are after .40 springs, the XRs are the ONLY choice!! They are great!!
(Late model meaning 2000/01 as I recall the tuner-guy saying.)
BTW..the least amount of preload you'll be able to use with the OEM washers is about 9mm. The flanges of the washers dictate that length. That's a bit more than I'd prefer..but reasonable. Certainly alot better than OEM!!