Microchip/Atmel have a new chip family based on 120MHz Cortex-M4. It has a lot of memory. We plan to use it in a product and so have posted it on our new startup site: alkgrove.com.
Some content added is:

• MicroSD with SAMD51 SDHC
• Microchip ATSAMD51 Development
• ATSAMD5x/E5x Family Datasheet Bugs
• SWD on the ATSAMD51

We also have a tool on github to help in developing C code for the SAMD51.