captfitz: I chose a 600w PSU, which should be good. Also, the liquid cooling is free, and it's made by AseTek. I don't know the company but I figure liquid cooling must be at least marginally better and if it's a free upgrade promotion, probably worth it, if only for the lack of a noisy fan.
It's not just the wattage that's important on a PSU, but the quality of the manufacturing (in other words, who makes it). A high wattage PSU made with poor components just means there will be that much more power frying the rest of the system's components if something goes wrong with the PSU. With regards to the liquid cooling, a few degrees lower temperatures don't mean much as long as the CPU is operating within safe margins. On the other hand, the mechanical components of a liquid cooling system (e.g. the pumps) tend to be under more stress than the small fan motor of an air cooling system, so will likely break down sooner (thus requiring a replacement, which is much more involved for liquid cooling than for air cooling). Additionally, depending on the manufacturing quality you could be dealing with leaks at some point in the future, which can mean just a small mess to clean up or possibly fried components to deal with (if the manufacturer was stupid or cheap enough to use an electrolytic liquid). Basically it's just a case of liquid cooling posing increased failure risks while not offering anything significant in compensation outside of very specific scenarios (e.g. extreme overclocking).