I replaced mine with Sumax. Don't know if the performance changed but the mileage is up over the past year that I've used them. But that is a pretty subjective thing as it could be the fuel or any other number of things.
I just bought an Ultima engine and had to change to a single fire coil. They say I need 300 ohm/ft suppression spark plug wires (graphite, spiral, etc)... My old wires are not metal core, but when I measured ohms from one end to the other, I get 7k ohms. I'm cool if I need to buy new wires, but that seems like a really big difference so I am wondering how I should be measuring resistance?