I would get the 620W just cause.. The 520 would be enough but still.. Quads use a lot of power and upgrade headroom is always good.. And you don't want to put too much load on it. It just like $20 more, worth it imo.
Also, I really wouldn't buy XP now if you're using a DX10 card.. DX10 games will start coming out in about a couple months and why waste $100 for two months of a slightly less buggy OS?
And I'm not really a fan of RAID0 since 1 of them dies and all your stuff is lost but it's ok if you don't mind risking it.
Other then that it's good