I used JK springs on an '03 X, but they were from a JK Unlimited Rubicon with a hard top. Those would have been the highest spring rate of the JK springs. The rear springs provided lift, the front didn't do a thing. While the rear JK springs will provide a lift on a TJ, you have to open up the top coil a bit for them to work on a TJ. The only way they are worth it is if they are free. The front springs don't do anything to lift a TJ.
The ride was fine. They are still on the X that I sold to a buddy of mine, he is perfectly happy with them.
These photos will show the comparison of JK springs to the oem springs on the X.
Rear, JK spring on the right:
Front, JK spring on the left, TJ spring in the middle, OME JK spring on the right:
There are so many different factory springs on the JKs, unless you know exactly what they came off of, it really is not worth the trouble. I mostly did it as an experiment, and it turned out ok for me. However, I used the OME JK front springs on that TJ X.
You also have to put the bar pin into the upper eye of the rear JK shocks, plus spread the bottom shock bracket somewhat, as the bottom of the JK rear shocks are a bit wider, if I remember correctly.