I have used CH version a long time a go which i did not really remember the feeling. Anyway, if you are comparing JP & SP string. I have used BG 80 JP & SP strings, all i can say is that JP string is more repulsive than SP string. I do not know how do JP & SP perform for other type of string.
I have tried BG66 Ultimax EX,SP & JP version I felt that the JP version holds the tension for longer than the EX and SP version.
For any difference u should consult yr stringer. As long as he is a good/experienced stringer, he should be able to tell when he is stringing them. My stringer said that the JP version tend to feel more dense n more thus more repulsive. But price-wise not really healthy for our pockets
Personally i think it's all marketing crap as i couldn't tell a difference between the JP, SP, CH and AS NBG98 string. The only difference i could see was the packaging.
Well, if i tell u its the same for all then u will never believe.. Go buy jp as its will mentally gives u the believe that its much better or giving that extra edge. Even the cardboard string packing from jp looks much solid... Paying more will metally telling its must be good
Up till this point there is still yet to be any conclusive proof and scientifically logical (single-blind test, double-blind test, all with exactly the same variables) test done with the comparison of the JP coded strings with the others. So the extra price difference might really just be the better cardboard packaging as you mentioned The only other significant difference I see is that Yonex JP has some models unavailable for the other codes such as BG66S and CBG100.
The best bet is try by yourself which string suit your gameplay most. For me, JP string has better gameplay quality than SP string for the same string type like BG 66 Ultimax JP is better than the SP in all aspect (durability, repulsion, hitting sound, etc.). Manufacturing quality must be the same. But there are some SP exclusive string which has good quality too like BG 66. Even the durability is low, it has become the most popular string in Indonesia (Great repulsion,control,etc.) The greatest edge of SP string is price. They have the best value for budget player. For better performance, JP string is the best especially for long run. Try both of them, so you can judge the differences. . . .