I love the internet.
I can comment on the Van's cover...I've used it many times in very high temps in AZ, NV, etc., on trips, and find that it does a pretty good job. I'm less worried about heat than I am about the direct effects of sunlight through the canopy. There have been reports of canopies focusing light and warping/melting items in the cockpit as well as the canopy itself.
I use the Van's for short-term stays, but for longer (overnights) where it will be on the ramp for an extended period, I switch the Bruce's cover for additional temperature control.