Brake Caliper thoughts...

Fishey

Racing brakes don't have dust seals and they have vented pistons.

In other news you can run your street brakes without dust seals on the track so they don't melt.

The reality is powdercoat isn't made for track temps but it doesn't mean the brakes are bad or won't hold up. You can strip the powder and send them to hard anodizing or like most people just accept the fact that they are going to look so-so.

Also, your rear brakes are not getting anything close in temp to your front brakes like not even in the same realm.

In all reality you would see a bigger improvement on the track with a racing ABS controller/bias then you would with a slight caliper upgrade.