iridium plugs?

[thejimrose]

i've been running them [ngk's about $9 ea at flaps] in the a4 [k04,
21psi spike] for about a month and i'm very impressed. car runs
noticeably smoother, especially under boost, than with the f5d's that
had a couple years on them. the engine guru here thinks that replacing
them regularly has a lot more to do with good running than the type of
plug.

my other engine guru [motorcycle fabricator / tuner /  mechanical
genius] swears by them.