I'd put the RAM on its stock timings for now, if thats 6-6-6-23 then fair enough keep it like that. Also underclock it to something like 400mhz instead of 500. You can turn it back up later, its just to eliminate RAM out of the equation.
So, 333fsb x9. Try 1.4v for that. If it's stable, you can lower it a notch and try testing again - repeat until its unstable then up the voltage 2 notches from that value. At 333fsb, 400mhz RAM will be on 5:6 which isnt bad.
If it's stable with those settings, try it again with the RAM at its usual speed (533mhz) or the closest you can get it on your ratio.
So, 333fsb x9. Try 1.4v for that. If it's stable, you can lower it a notch and try testing again - repeat until its unstable then up the voltage 2 notches from that value. At 333fsb, 400mhz RAM will be on 5:6 which isnt bad.
If it's stable with those settings, try it again with the RAM at its usual speed (533mhz) or the closest you can get it on your ratio.