The EFM32 is impressive, but I think I'm going back to the Freescale part for now. The bootloader is a big thing for me, and while the EFM32 USB-CDC and xmodem protocol is easier to use from a software standpoint, the KL27's HID protocol is driverless under all OSes. Plus it opens another possibility: firmware loading through a driverless and OS agnostic Chrome plugin using the Chrome HID API.

It's another arbitrary challenge in this project, and that's great.