Which Spark Plugs?

[bris09]

Engine is a 2.5. Bored .20 over, P&P head, +1 Exhaust valves, TU SS Header, Custom 1-piece intake (raised plenum, P&P runners), 52mm TB, Water/Air intercooled, Stock TII turbo w/ .63 housing, TU 3" swingvalve, and 3" exhaust. Also has TU Billet fuel rail, AFPR, and one of Paul's cals set for 20psi of boost. I'd prefer to use a NGK Iridium plug. I'm assuming I want a colder plug just not sure which one to use.

Thanks

[GLHNSLHT2]

I like my Autolite AR51's. They're as cold as RN6 champs but run fine on a stock engine even. They have a cutback electrode for better flame propagation.