[eschaider]

Roush dynos their crate motors, like yours. When they go through their tuning process, on the dyno, they will use different heat range plugs until they get the kind of power curve they want.

If you call them they will share this information with you as the owner or even as a potential new owner of one of their engines. At that point you will have the plug that worked best for Roush on the dyno. If you wish to experiment with hotter or colder heat ranges from there, you will have an excellent starting point to work from.