Power Macintosh G3 (desktop)

I got my unit from the same recycling as Power Mac 7300 and it comes from the same editorial. It's in good condition, maybe except power switch whose springs were broken. It's not a critical failure, but it makes power switch act much quicker than with good springs.
 

Overclocking

Overclocking is quite simple, as it requires only jumper manipulation. Remember that this not only voids warranty but may prevent all service procedures of the unit! So if you overclocked and have bad blocks - it's your fault. If you have crack on power switch - it's your fault. If big Godzilla jumps from the unit - it's your fault.

Near the battery, there's a 9-jumper block J16 with sticker "Warranty void if removed". These control CPU bus frequency and multiplier. Just configure it according to the table. Usually one step is enough, so 266MHz units may run quite well at 300MHz without changing bus clock, they sometimes suffer small overheating. Changing bus clock should be taken as last resort, as it clocks all components too.
Another component which may slow the computer down is the backside cache, which always runs at half of CPU speed. If you overclock 266MHz to 300MHz, the backside cache will overclock from 133 to 150MHz. If it's made of poor chips, it may make system unstable. Finally, overclocking from 266 to 300MHz gives about 10-15% increase in performance.