Mcdermd has been hosting this really great website,

It Breaks down the Models and has info on how to over clock

http://www.applefool.com/clockchipping/

So far my favorite over-clocked machines are:

LC-III -(25) -->33mhz

http://68kmla.org/forums/viewtopic.php?f=9&t=19430

Macintosh IIsi -(20) -->25mhz

http://68kmla.org/forums/viewtopic.php?f=29&t=17923

Quadra 605 -(25) -->33mhz

http://68kmla.org/forums/viewtopic.php?f=8&t=19310'>http://68kmla.org/forums/viewtopic.php?f=8&t=19310

LC-475 -(25) -->33mhz

http://68kmla.org/forums/viewtopic.php?f=8&t=19310

Quadra 700 -(25) -->28-32mhz

http://ftp.nluug.nl/ftp/pub/pub/infomac/info/_Hardware/quadra-700-clock-mod-145.txt

There was someone on this forum that did this oc with pictures but I cannot find the thread!

Quadra 840av

Mcdermd --- Wanna oc this and make a Thread?? 48mhz????? ! Heck Yeah!

Powermac / Preforma 6100 -(60-66) -->90mhz

http://68kmla.org/forums/viewtopic.php?f=12&t=20392

Quadra / Preforma 610 -(20) -->25-30+mhz

http://68kmla.org/forums/viewtopic.php?f=8&t=20386

The LC-III is by far the easiest to OC, you just remove one resister and relocate it on the bottom.

If you have any other threads or info you want to post please do!