mine started misfiring at 220kw.
was fine at 200kw.
standard ignition system, besides ngk leads, which were quite new anwyays, with heat range 7 plugs gapped at 0.9mm

currently using (suggested by slaz, and not looking back haha) motec CDI, external, crane coil, magnrecore custom leads, and heat range 8 plugs gapped at 0.7mm.
currently pushing 250kw and no problems or misfires, what so ever.
also using a s300 ecu.