Step 1: change the jumpers on the logic board to either change the bus speed or the multiplier.
Step 2: go to step 1, repeating until it starts crashing.
Step 3: back the clock speed down a fair bit from the precipice.
Step 4: if this doesn't give you the boost you need, add a high-end cooling system and faster RAM.
Step 5: cringe when you realize you've spent more than it would have cost to simply buy a new machine that's faster.