2011 5.0 GT with a few basic bolts ons that belongs to my cousin. 1/4 mile times are 12.1. Its primary use year after year is NHRA bracket racing.
Summer months around here are hot and humid, 90 to 100+ deg. He uses Motorcraft 5 20w synthetic blend in it. I think 5 20w is great for mpg but not the best for smokey burn outs and full power to the red line pulls in blistering heat.
I suggested 10 40w full sythetic but since Ford says 5 20w of whatever a sythetic blend is he wants to use it.
I use 10 40w Mobil 1 in my supercharged C6 Corvette. Both cars are stored from fall to spring.
What do you use for hard use in summer heat?
Ford doesnt always know what is best.

 

I use Pennzoil Ultra Platinum 5W20 all year round, but then I don't race my '06 GT 'vert.

 

You could use 5W30. It'll have the same viscosity as 5W20 for cold starting but maintain a slightly higher viscosity when hot.

 

I've read on several oil test, 5W30 thins to 5W20 in hot engines. I've never been able to find what 5W20 thins down to. I use 5W30 in my v6. Don't feel warm and fuzzy about 'synthetic blend', there is less than a cap full of full synthetic oil mixed in the bottle

 

My 2014 owner's manual say to use 5W50 if you operate under extreme conditions such as track use and drag racing. Assume there will be some drop in fuel economy as a result. I use 5W50 just for the sake of longevity.