Firstly, I'm not a fan of magnatec. It seams like a bit of a gimik to me. What I say is just warm you engine up a bit before you take off and thats plenty.
Secondly, I am a big believer in synthetic oil for newer engined cars.
I've heard that castrol synthetic R 10W-60 is really good. In melbourne theirs a place called RacePace Motorsport that build (not import modified and retune) 600 plus kw GTRs etc etc that have a real reputation for nissan engined cars and they swear by castrol synthetic R 10W-60. And thats good enough reason for me to use it...
Other than that, Mobil 1 synthetic 0W-40 is also very good.
Mineral oil tends to brake down in terms of carbon to carbon chains (year 11 chemistry) when under high temps and pressures which is what turbocharged engines go through. They lose their lubricating properties once it starts to brake down and that?s prolly why you hear of engines lasting along time with synthetic....
That?s my understanding and explanation for it anyway
However, On my daily driven old l20b datsun, I'll stick to mineral based oil. I've read that for older engines that havent been rebuilt etc that synthetic is a no no