WP Replacement Springs

No difference, just depends on if you need a even or uneven last digit like 45nm vs 46nm.

Some say Ktech is tested better to be more in range for actually spring rate its labeled with. Could very well be that OEM varies slightly more since they might prioritize economy slightly more.

Just pay attention to the conversion factor. Some use N/mm and others use kg/mm.

I worked for a large reputable suspension shop, and we rated every spring personally before installation. WP springs varied widely based on what they said they were. We did have the best luck with K-tech as was mentioned. We also found RaceTech springs would destroy and score up the inside of the fork tubes. Just about all the manufacturers used different ways to get their "rate", so trying to stick with the same manufacturer when testing different rates can be beneficial. That way you know they were at least rated in the same manner. 

This may be of use for spring rate Equivalencies, with the 3 main ways of describing / labelling them:

 I wish I could recall who I got this from - apologies ( and thanks)  to whomever it was.

I’m really liking the KTech fork springs I have installed, the polish is nice and they have been correct/consistent on the spec length

I have not had their rate checked so I can’t comment on that. 

Right from KTech USA, they are in NY also, so I usually get them delivered in a day depending on what time I order 

Wp springs break…buy FC springs, lifetime warranty….

I've had good luck with Diverse Spring. I heard they made springs for some of the bigger name companies.

https://www.diversespring.com/motocrosssprings/