18 Mhz IIgs?

[Charles <spammeister12345@aol.com>]

Ok, I'm scanning the Apple II websites and I run across this one:

http://applemuseum.bott.org/sections/computers/IIgs.html

A quote on this page says:

The Apple IIGS was, and still is, the most impressive Apple II ever 
produced. They were introduced in September of 1986, and ran a much 
better processor, the Western Digital 16-bit 65C816 (compatible with 
6502) running at 2.8 MHz. With third party hardware it can now go up to 
18 MHz.

What?  Who is running a IIGS that fast?