Newegg's is overblown and useless from a technical standpoint. The most tried and true one I've found is this one:
eXtreme Power Supply Calculator
You'll get vastly different results from this one vs the Newegg one, which sadly, is geared more toward their vendors than helping you pick a cost effective and efficient power supply.
100 watts more than what Newegg states is overkill, especially since their estimator already over-estimates. For most users and most systems, it isn't necessary. If you're "buying ahead" for gamers and system tweakers, then absolutely.
In this case, the 420 watt would be fine. I have a system very close to what you're using at home (sans the GPU) and my wattage needs are filled fine by a "mere" 420 watt power supply as well. The "more is better" mentality isn't always the case for power supplies. The one you've linked, Lippy, should be fine.