Hi,
I'm not sure anyone will be able to help you, but kinda the same rules apply for PC overclocking so the results might be:
1) The device won't even start, you will have to reset the CPU clock to stock settings.
2) The device will start but the OS/apps will be unstable (more crashes than usual, device rebooting itself etc).
3) You will be fine.
4) If 3) applies, you will most likely experience higher battery drain since the CPU will require more power.
You will have to ask about speeds somewhere else I suppose.
Filip