Never used anything other than Champions in my four RRC's over the past 17 years, also several series LR's plus many other vehicles during my 50+ year 'driving' lifetime.This period has encompassed ownership of 4, 6 & 8cyl. engines & I've very rarely had a problem, despite the plugs often exceeding the specified replacement mileages. All my vehicles have been bog standard & I accept that modified/highly tuned engines may need uprated plugs. Interestingly I bought a 3.5efi Classic around 13 years ago & the maintenance invoices revealed a surprising number of replacement plugs to cure misfiring problems. Having checked the part nos. on-line I found they related to both NGK & Bosch products. The final set fitted had been Champs. & the car was still running well 3 years later when I sold it on.