Nissan (and all other car makers) engineers spend at least a little bit of time and money figuring out which oil viz works best in each engine. Plus they have a lot of experience. And engines are a LOT pickier than they were back in The Good Old Days of iron blocks and carburetors. I'll go with what they recommend.
But, as mentioned above, a few cSt here or there on the W end isn't going to make that much difference. But you can go too far.