i think i remember gaara speaking of some issues running at 300+FSB
. my best advice is to go back to the drawing board and work your way up from 2.0GHz and 1.35v. keep boosting the FSB, testing and upping vcore if necessary. use a divider to keep your memory at BELOW DDR400 to eliminate that as a cause. keep an eye on the HT multiplier so that your HT stays very close to 1000MHz. you want it near 1000MHz, not too far above in case that causes instability and not too far below in case it was the HT causing the instability (so that if it's still unstable you will see).
what cooling are you running? what have the room temperatures been like? what voltage is your memory?
as for a good setting for 2.4GHz try 1.35V Vcore, obviously 240MHz FSB and a 5:6 divider (for the moment, that will put your memory at exactly DDR400). if your X2 is as good as you said it was stock Vcore for 2.4GHz should be fine. if not just run it up to 1.4V (personally i wouldn't feel it's worth using any more than 1.4v for 2.4GHz).