Ideal if you want to upgrade your CPU card to almost double speed. Note that most cards do support this but some cards may not run stable or at all at 80mhz (e.g. the A3640 (the only one I know of actually, but do check)).
You'll have to change the oscillator and the CPU. If your CPU is socketed it's a trivial operation. If not you can try to unsolder it if you're brave enouph. I have done that to upgrade a Blizzard 1240 to a 12608-) though I'm still waiting to receive a 66mhz crystal to finish it. But there have been reports of people doing it just fine (note that soldering the CPU is advised for people with a lot of soldering experience though, to be honest. I should know it, I damaged some tracks in the process! ... they were easily repairable though).
These 040's are somewhat harder to find and I'm not putting the price too high. Remember it's the 40mhz version, and the 80mhz crystal is included.
Check it out
HERE [EDIT]
Note: Some A3/4000 cards don't require changing the oscilator to do this.
