Here's a different perspective
My wife Jeanine and I built our RV-6A for travel and cross country air racing. The air plane is based at Fayetteville, Arkansas (many days over 100 F). It has a sliding canopy commonly called a "slider" in the RV world. The canopy is stable at all times in windy conditions during ground operations. When the canopy is open it is just like sitting in a convertible car with the top down and when you start the engine you get a nice breeze during all operations on the ground with an effective windshield to keep the direct blast off of you. Before you takeoff you must close the canopy. The fresh air vents do a good job of keeping it comfortable (more on this later). There is a light weight retractable shade available, which we installed, that is very effective for controlling direct sun heat and glare on bright sunny hot days.
Ok back to the vents. I developed cover plates that I mount in the NACA vent openings for racing to reduce drag. Under some conditions it is very uncomfortable in the cockpit with those vent covers in place. It makes you realize just how effective the vents really are when you don't have them. In the cockpit we have the aluminum "eyeball" control outlets and at cruise altitude I almost never leave them fully open.
I think this configuration (slider, retractible sun shade, fresh air vents) is very effective. I have no experience in the other configurations.
Bob Axsom