Go through the first two threads. Do not do anything until you have a good idea about what you are trying to do. Once you have definite questions (you will, you will ), come back and ask.
Keep in mind that these are guides, not cookbooks. YMMV. Your Mileage May Vary. Because of all the variables, you may not do as well as someone else with a similar system. Or you might do better.
Overclocking since 1978 - Z80 (TRS-80) from 1.77 MHz to 2.01 MHz