The effect of removing wheel covers

I left the wheel covers off because I wanted to drive to work and back and make it quick to re-torque the lug nuts. I don’t necessarily like the black wheel phenomenon of the last 15 years it seems, but the wheels underneath these wheel covers aren’t bad. I’m thinking about some Center caps. For 2014, what size are the caps? also do you give up much gas mileage in the aerodynamicy lost in removing the wheel covers?

As always, thank you scholars for the lively discussion.