For a track-driven car, our advice is to always remove the splash shields. They trap far more heat than they do protecting anything from heat.
A much better solution for ball joints would be to install a thermal barrier over them. We offer a product called Teknofibra that is an incredible thermal barrier. You can hold it in your hand and put a blow torch to the front side without feeling the heat. This is not your grandmother's gold foil heat shield!
We provide a lot of this material to professional racing teams for various areas of the chassis. They stick it everywhere. It comes in a couple different thicknesses of 'felt' backing. It It's not cheap, but there's nothing else out there quite like it. You can
see Teknofibra on our website here.