Whats the most realistic speed I could get from a ...

[Flash]

P4 2.26ghz on air with stock intel fan

I managed 2.8Ghz at 1.55v but was unstable and BSOD'd a lot so didnt push any further

[Ethos]

All depends really, can't just guess a speed.... you could try increasing the voltage and check the stability again

[Nox]

i take it thats a 533mhz bus chip, and does your mobo support 800mhz by any chance? As Ethos said, everything depends a lot on luck, though the current intel chips you would have to be unlucky to get a 2.4 or 2.6 which didnt get to 250mhz with stock cooling...

Nox