This was tasted extensively by Jayz and Gamers Nexus which if I'm honest hits on good points but the results are neither here nor there. As a general rule if you have a GPU it's wise not to feed it pre radiated (warm) air and don't restrict its air feed. I'll always put the rad as an exhaust and give the GPU an extra fan in the back of the case to help get rid of that heat.
Let the case do the work. (case dependant obvs) I'm still waiting on my meshify front panel for the Define C as the stock front is restrictive.