Warranty up? Your powertrain warranty goes 5 years or 60k miles. Therefore, in case you don't want to risk Nissan denying a warranty claim, do not use Castrol 0w30 here.
However, chances are you won't have an oil related problem, or they will only check to see the oil is relatively clean and the valve covers are clean, sometimes all they check.
Technically that oil will work very well in a Maxima. It has some of the best overall specs it meets, so its better than SL or SN, in reality.
Great looking car. How has the CVT held up? I always hear about trouble with those.