I have a Ca18det powered nissan bluebird attesa. It is producing around 250hp at the crank as it has had some mild modification. The engine is in good nick considering 150,000 kms. I would assume this is a large ish power:displacement ratio. I am about to upgrade to some serious oil as now im a little more clued up on it than i used to be. Thing is you guys know everything there is to do with oils and you guys can sort me out. Im in New Zealand where the average temp is 15 degrees C and the car will never see a cold start lower than -5 C. Never. Half the time the car will see street driving and low ish street oil temps. The other half will see some moderate and some WOT. I want the best possible protection (as anyone) for this condition but also to serve the low oil temp situations aswell. Hopefully im on the right track with this... I am thinking Redline 10w30 or 10w40. The cost does not have a say in my decision. The change interval does not concern me. I want the engine to last. Oil is expendable. I have also considered Castrol RS/Castrol Formula R 10w60. This is a really viscous oil at operating temp. I assume this oil is designed for mostly high temp work, not suitable for street driving temps? Please help me out in my decision. Should i be going for a high vis or a low vis for my conditions, the more i read the more i get confused! Thanks for your time.