I've never used anything but premium in either of my QX's. I can't remember what the fuel door says - maybe premium fuel recommended? I think it may have been "required" on my QX56 and maybe just recommended on my QX80. Either way, I figure it's safer to use the higher quality stuff. As much as we fill the tanks up on these things, it probably could be a meaningful amount of savings to use a cheaper grade. But, I figure if I own one of these and I'm worried about saving some $$$ on cheaper fuel, I probably shouldn't have bought such an expensive SUV!
In any case, welcome to the forum. We're not a terribly active crowd here, but those of us that are active here will be happy to answer any questions you may have that we have can.