I would also say to stick with the 600W the more power you have, the less problems you have to worry about not needing enough power.
Example of not having enough power would be me. I have a 400W PSU for a Q6600, 8800GTX, 4GB ram and a HDD, if this PSU blows, under load, then you whole system will short circuit, which means, you need a new rig. So more power, the safer, unless you spill water over it
