Here is a SweetFX profile i have made up for GSC2013/Extreme.
It has been tested on V1.15 on an I5 4670 and ASUS 4GB R9 290 Direct CU GFX card.
I notice no appreciable drop in framerates, but as always, your mileage may vary.
I love the sim, but feel that the night races are a bit too light for my tastes and the daytime is a tad washed out.
Please read the readme for install instructions and MAKE SURE you make a backup of the d3d9.dll file in your main GSC2013 folder before installing this mod.
The mod can be turned On and OFF with the Scroll Lock key on your keyboard.
This is the first version, so all feedback good or bad is most welcome. I hope that you enjoy and thanks for an awesome sim !
Alternate D/L link @ :