I have a stock cooling fan, stock fan shroud, stock oil cooler, stock thermostat, stock water pump with no bypass blockage mod. I never got around to reinstalling the aluminum undertray but it doesn't seem to matter. I do run the turbo oil pump. I run right at 200/200 water/oil temps. I am not convinced that one needs all of this expensive gear to run a 13B at race pace.

As far as the oil cooler robbing power, I really don't think so. The oil pump is going to be turning at a set speed for a set RPM anyway. It's the oil pump that robs the power. The 2nd gen comes with the oil cooler stock. The car is underweight anyway. You might as well keep the oil cooler.

My experience is that Mazda did a great job on this engine straight from the factory.

Later,
Gruff