I would ABSOLUTELY go with OEM. In my opinion, there is no reason not to. You can choose the right grades with OEM bearings as well. I don't think any aftermarket companies have that same grade system. Engine building is tedious, and the more exact you are the better off you will be. Although the bearing grades from the factory have very minute differences, I think it is worth it to choose the specific grade Nissan designated for your engine.
I think the whole set (rods and mains) was like $130 from Z1 just a few months ago. And they will give you whichever grades you ask for.
Make sure you plastigage before you put the oil pan back on
