"Wicked fast" at a then astounding 40 megahertz. Interesting to note is that when Apple said 40 megahertz in the eighties and early nineties, they really meant it. That speed referred to both the main logic board clock, as well as the processor speed.
The IIfx not only featured high clock speeds, but special dedicated processors for sound and serial communications, as well as speciallized high-speed RAM.
The IIfx was the final development of Apple's 68030 machines, and was replaced at the top of Apple's lineup by the Macintosh Quadra series. mestic
An interesting curiosity of this machine was its I/O chips, which featured a pair of embedded 6502 CPUs, meaning that this Mac also had the core of two Apple II machines inside it. However the machine's architecture did not expose these CPUs to user's code.