1K Ohm Vrs. 5K Ohm? Difference is..?

[Steve Gutman]

And can they be mixed? Are they vehicle specific?

The details:
I have been chasing idle and drivability problems for years and I changed the plug wires awhile back. With a Euro SL the battery is in the engine bay so they use some 45 degree plug cap ends to clear the battery tray. I moved a heat sheild and used non-MB wires. They are marked 5K, the originals are 1K. I want to get the 45 degree plug caps and realize the new wires could be part of the problem.

I don't know what the resistance is for.