The HuC6280 8-bit microprocessor is Japanese company Hudson Soft's improved version of the WDC 65C02 CPU, an upgraded CMOS version of the popular NMOS-based MOS Technology 6502 8-bit CPU.
The Mega II contained the functional equivalent of an entire Apple IIe computer (sans processor), which, combined with the 65C02 emulation mode of the 65C816 processor, provided full support for legacy Apple II software in the Apple IIGS.
Bill Mensch pointed out that Fmax depends on off-chip factors such as the capacitive load on the pins.