Better holding your finger than pulling it. :Q
What speed RAM do you have?
To get 2.8GHz you need a FSB ov 350MHz. I'd say try that first without boosting any voltages. If it runs stable, you're done. If it runs, but is not stable, then you need to find out if it is CPU or RAM holding you back, by running stuff like Memtest and Prime. Then, boost the appropriate voltage. If it doesn't run at all at that speed, then start by lowering the RAM multiplier and increasing latency.