Upping the FSB will increase heat output. The CPU will draw more watts and all those watts will become heat. I think you could still do it on the stock cooler.
70c is perfectly safe for a 65nm Intel quad.
And as for which is correct for the TJmax, it doesn't matter, don't look at the core temps, look at the distance to TJmax, those readings will always be correct. Try to keep them below 30c-35c.