I already have the GSR radiator in my car..
And the valve cover DOES make a significant tempature rise in the engine bay. I have a thinner cover that original so it´s gets "hotter" that the OEM

I´m about to install Mugen thermostat and Mugen Thermoswitch, also to wrap tempature bandage on the header and install a vented hood..
Hopefully this will help of a bit..
But in anyway I wonder if there is a more powerful OEM radiator on the market..