I guess I'm slack. I've always used a spark to judge the ignition. It doesn't take much of a spark to run a KX. I ran with a weak spark for years. I guess I missed the question as I am dodging from this site and work at the same time. Resistors are there just to reduce electrical noise from the coil/wire/plug from interfering with the CDI. I've never really pushed the issue, as I don't have a stock ignition system. It has no resistor. My previous ignition system had one. And like all, they are 5k. There is no performance loss with using a resistor I don't believe. I could be wrong.
As for my comments on caps. If you suspect a cap, replace it. Half the time your cap is going to read 0 like mine and like my old stock one.