NGK R5671a-8

NGK, 5 heat range, & projected tip plugs are the place to start. Ignition curve, as others have suggested.

The enemy of det is heat. Make sure your engine runs as cool as possible. The temp on your gauge tells you what the temp is at the sender, not near the exh valves where the coolant might be experiencing localised boiling. Cold air induction can also help, as well as increasing HP.