Step 2. Overclocking your Desire Z using the Godspeed method
(safest way, keeps stock rom and mac address)

1. You will need a custom recovery to back up (image) your phone. I would not skip this step.
By creating a nandroid backup your are essentially creating a fallback in case anything screws up. Don’t skip this step. 


Go to Market on your phone and install Rom Manager (free version is fine).
Open the app and press Flash Clockwork Mod recovery. it will ask "Confirm phone model: HTC G2", tap yes (thanks for the tip stridger !!). 

When finished, it says "Successfully Flashed ClockworkMod Recovery!"
I recommend rebooting the phone after flashing the Recovery.
Now let's test it:
From ROM Manager, tap "Reboot into Recovery", it will ask "Are you sure you want to reboot into ClockworkMod Recovery?", tap OK.
Inside ClockworkMod Recovery, use the trackpad to navigate and select an item, or the volume buttons to scroll,
and power button to go back.
Select "Reboot system now" to exit ClockworkMod.
If ClockworkMod Recovery doesn't start and you see a red triangle with an exclamation mark, flash it again.
Sometimes it requires a second flash to work properly.


2. Go to
here to download gtrab’s Godspeed update that will overclock your phone.


You can choose 3 speeds: 1.0, 1.2, 1.4 GHz

I chose 1GHz as I was only looking for a slight boost.
The higher the clock speed (with same voltage) the higher the temp and stress on the CPU. Your choice. All 3 work fine (on most Z’s). 


3. Rename the godspeed.zip to update.zip
Copy the zip file to the root of your SD. Don’t extract it.


4. On your phone go into SETTINGS-->APPLICATIONS. Uncheck Fast Boot


5. Now hold power button and select Power Off this time.


6. Next, hold down the volume down button and keep holding while you power on the phone.
You will boot into recovery. A green and black menu should come up (otherwise you may need to reflash clockwork recovery again).
Use the optical pad and scroll to backup and restore and click to select. Do a nandroid backup. It will take a few minutes.
You know have a back up of your phone in stock condition plus root.
In case you screw up anything you can always boot back into recovery and restore from backup to revert back to stock. 


7. Go back to main recovery menu after the back up is complete.
Choose apply update. Choose the update.zip that your transferred to your sd card on your phone. Reboot when done.
8. You will now have an overclocked phone running a stock ROM. 


9. Install SetCPU (optional)
This is an excellent app to control the clock speed of your CPU based on demand. It will scale down your cpu when not needed and allow you control of how fast you want it to run in different situations.
It is not free but it is not expensive either and worth every penny.