INCREASE SPEED BY ACCELERATING THE CLOCK?  (3.2)
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       Apple engineers designed the Mac IIsi to run at 25 megahertz.  
  Apple marketeers made them reduce the speed by 20% so as not to hurt 
  sales of the IIci.  Thus with various caveats it is generally safe 
  to accelerate a IIsi to 25 Mhz by changing the clock chip.  All 
  other Mac models were designed to run at the speeds they normally 
  run at so "clock-chipping" them is a much iffier proposition.  
  Compact Macs, PowerBooks and the Mac II, IIx and IIcx as well as 
  the LC and LC II use the same oscillator to time various external 
  circuitry as they use to time the CPU so they almost never work if 
  the clock chip is replaced.  Most other Macs seem to work for at 
  least a while when sped up by as much as twenty percent.  Somewhere 
  beyond a twenty percent increase in clock speed most Macs experience 
  serial port problems though the exact level of safe increase varies 
  from Mac to Mac even within the same model and configuration.  Other 
  problems may surface over time as the extra heat generated by the 
  faster speed increases the wear and tear on the insides of the Mac.

       Performing this upgrade is not for the faint of heart.  It is 
  quite complex and requires soldering, replacement of several parts, 
  and other non-trivial procedures.  If done improperly it can result 
  in major, expensive damage to your Mac.  I am not going to give 
  detailed instructions for doing this here.  If you do want to do 
  this yourself, several text files are available at the usual ftp 
  sites that outline the procedure.  For people who are willing to 
  open their Mac and swap out RAM or a hard drive but don't feel 
  comfortable soldering on their motherboard, KS Labs, (614) 373-0353, 
  offers $165 kits that more safely (no soldering) accelerate the 
  clock.  These kits include a clip-on oscillator plus a heat sink 
  and fan to keep the faster circuitry cool.