Appreciate it! As of this writing, 10w-40 is the thickest oil, that I feel comfortable with. The manual for this car states 5w30, 10w30, and 10w40, conventional oil. It also seems like synthetics get eaten up quicker with this motor. The full conventional oils did not consume as much, as the synthetic blends.
Will look into the 15w-40 for a VQ35DE. I'm sure it has been done before. If my current Chevron Supreme 5w-30 synth blend burns up too much, going to look for a thick 10w-40, or 5w-40, that doesn't shear down easily, (Rotella?). The GTX 10w-40 seemed like a thick-ish 10w-40, and did the best compared with the various oils that I have tried with this engine, no doubt.
When I owned my VQ35de powered cars two of them were aftrmarket forced induction ( 2x 350Z, one with a Vortech and one with a ProCharger running 389 and 411 whp respectively).
I always ran Mobil 1 15w-50 with those.
My other VQs were 5w-40 or in winter 0w-40
I was a huge VQ guy for many years, onwed two 350Zs, three G35s.