IMO it's a waste of money to upgrade to F8x calipers.
Also, track pads on stock rotors (which is what the Zimmermans are) will make the rotors heat quickly because they aren't suited well for a harsher pad, especially with longer braking zones. I ran a similar setup and my rotors would get hot QUICK.
For heat management, you can create ducts (many options on here) which can allow you to go longer without going up to a BBK. I would also recommend upgrading to a two-piece rotor setup to replace the OEM rotor. Girodisc still makes a decent replacement setup that I've used, as well as Paragon.
Here is a link to the Girodisc rotor:
https://www.bimmerworld.com/Brakes/B...C7UHysVIxTwRhV