For the price on that 700 watt PSU you cant do any better, even most 5-600 watt PSUs cost more, while you dont need that much power you cant beat the price so i would stick with it.
probably not now, but i plan on adding 2 tv tuners in the future, and probably will be spinning 3 or 4 hdd's, so i just figured id go a little bigger than what was needed. (by the way, im not even sure what the draw is for tuner cards and hard drives, just wanted to be on the safe side)
btw that site is cool... it put me under 300 watts, so i know 700 is overkill but i guess it leaves me room to expand in the future