The SiFive HiFive Unleashed has quad RV64GC plus one RV64IMAC and runs at around 1.5 GHz in TSMC 28nm -- mine's a little unstable at 1.5 after three or four hou

The SiFive HiFive Unleashed has quad RV64GC plus one RV64IMAC and runs at around 1.5 GHz in TSMC 28nm -- mine's a little unstable at 1.5 after three or four hours at full load, but it's perfect at 1.4. It was pricey at $999 because the chips are from low volume "shuttle run" aka MPW production (probably $300 or $400 each -- would be maybe $10 in volume production) and the board has 8 GB DDR4 2400 and other expensive things such as FMC connector. But it's well faster than a Pi 3 and I've had 2.5 years of use out of it already...