It has been argued with the 300V you can put oil changes off till 10k, though I'm not suggesting it, just mentioning it. If you want full synthetic while staying with motul try the 8100 series (like the x-cess 5w-40), cheaper than 300V. 10w-60 hot rating is just too thick for a skyline, even 10w-50 hot rating is too thick imo (although since the engine has done 160k I still wouldn't use a 50 unless it was leaking oil). As for turbolight 4100, it's an ok semi-synth, about 75% synthetic I've read.