Currently The fastest Arduino compatible development is hifive1 with 320Mhz RISC-V MCU. This board family will be have 400Mhz Cortex M-7 MCU.
Key features of MCU:
- 400Mhz 32-bit Arm® Cortex®-M7 core with double precision FPU and L1 cache
- upto 2Mbytes of Flash memory
- 1 Mbyte RAM
- 4 DMA controllers
- Up to 35 communication peripherals
- 3× ADCs with 16-bit max resolution
- 2× 12-bit D/A converters (1 MHz)
- Hardware JPEG Codec
- Up to 22 timers and watchdogs (upto 200Mhz)
- RTC with sub-second accuracy & HW calendar
- Cryptographic acceleration*
and lots more

Board Feature:
- Arduino UNO/MEGA form factor
- SD-card with card detect feature
- optional QSPI Flash upto 512 Mbit (133Mhz)
- USB OTG
- CAN Interface
- Ethernet*
- Camera Interface
- Battery Charger
- SWD Interface
First PCB layout for Concept and hardware Verification is ready :)