You should not only consider performance but also readability. Calculations in Blueprint turn into spaghetti in no time while it can be a few lines of C++ while the flow of game logic is easy to follow in Blueprint compared to C++.
I suggest you use both for pretty much everything. Make a base C++ class declaring all the variables and assign them in Blueprint and add logic in Blueprint and calculations in C++. Also remember that you can’t make anything truly private in Blueprint so you quickly end up with a Blueprint with a ton of “private” functions exposed that you have to scroll through.