Must be something in the air or the water over there as the Nismo cap, stat and Koyo rad works well over here with no issues. Not any huge differences to be had granted, but every little helps as every degree is a prisoner.
I also experienced a reduction in engine bay heat soak with my fans coming on earlier and switching off later as cold air was sucked into the engine bay for a longer period.
Channeling all the cold air to and from the rad directly into the engine bay by filling in the sides also helped, as did a proper vented/scooped bonnet allowing cold air in and hot air out. Also removing some of the plastic at the bulkhead also helped by creating a larger gap to allow the hot air out or if you are feeling flush then a raised Du Luck bonnet works very well.
Serious modification of the front bumper also helps, but that is a story for an other day
Normally, you should not experience heat soak or running hot issues with a na car. I run 600 bhp and it is a constant battle keeping the car cool on serious track days and I am continually making subtle changes to try and improve the situation but I am slowly getting there. Mapped to run a bit more fuel through on the overrun also helps quite a bit by helping to keep the Turbos cooler.
I could go on forever but I don't want to give all my secrets away
Alex.