These work pretty well in a race application (not for street use).
http://autolite.test.foresitetech.net/node/430
But with the kids and recession, my budget isn't what it used to be.
I use Autolite 3924s to good effect in my car but I run Magnum style heads. They might be different than X,J, etc.
Never had a problem with NGKs either. I really like the way they work with nitrous.They seem to be easier to read than Autolites. Not sure why I went back to Autolites when I went Mopar, but whatever.