Here is another platform suggestion that is geared at music makers / synth diy types, but has a good spec M7 @480MHz inside.
and it claims Arduino support.
I have this DIP version so would be happy to test out a uLisp port on it and report back if you are interested?
I was immensely disappointed they dropped the advertised MicroPython implementation after I bought it…
Interesting board though.
spec summary paste ==>
Stereo audio IO - 96kHz / 24-bit audio hardware (AC-Coupled)
Programmable in: C++, Arduino, Max/MSP gen~, Pure Data
x31 GPIO, x12 ADC inputs (16-bit), x2 DAC outputs (12-bit, DC-Coupled)
ARM Cortex-M7 MCU, running at 480MHz
64MB of SDRAM for up to 10 minute long audio buffers, 8MB external flash
SD card interface, PWM outputs, and various serial protocols for external devices (SPI, UART, SAI/I2S, I2C)