I also have 2017 Nismo Tech M/T. We hit 86F last week and I got up to 230 on oil temp. City and Hwy, some stop and go. Never got higher.
Did not notice power loss. I also run 94 Octane, so that may help a little.
As for oil. As another poster mentioned, GTR oil is not same. However, it's not just any 5w30 for our Z's. Per the book, you SHOULD use Esther oil. Either the Nissan cool-aid (good for keeping warranty hassle free) or REDLINE 5W30.
Not to say you cannot use any good synthetic 5w30, if you do your homework, you will see that our engine has coatings (DLC or Diamond Like Coating) that are supposed to work with TRUE synthetic Esther oils.
https://www.nissan-global.com/EN/TEC...RVIEW/dlc.html
The brand of oil or quantity of oil will not affect your temperature. Just keep maintained.
Otherwise, your temps are fine.